Developing pawns isn't as important as developing pieces, while you develop the pawns, you create queenside weaknesses that your opponent can try to use against you.
Ruy Lopez / Morphy Defense
Developing pawns isn't as important as developing pieces, while you develop the pawns, you create queenside weaknesses that your opponent can try to use against you.
which weaknesses? how to exploit them?
CallMeMisha shows a game in which this is a good move, what are the differences?

Usually 4...b5 transposes to the mainlines anyway. The reason 4...Nf6 is prefered is because it is more flexible. Black hasn't commited to b5 yet, instead he develops a peice and waits to see what white is going to do.
Pawns can only move in one direction, so every pawn move has strengths and weaknesses. The difference between the early 4 ... b5 and the later 6 ... b5 is that Black has developed two more pieces and has the vulnerable f7 square protected. Theoretically after 4 ... b5 5. Bb3 Nf6 6. Ng5!? attacks the f7 square and how does Black defend?
Often lines with 4 ... b5 and 6 ... b5 can transpose into equivalent lines but a well prepared player can take advantage of slight differences in move order.
I would not advise you to play the Ruy until you are a very strong player already. The theory is immense and the positonal play is very, very deep.
Thanks for advice
But I must learn how to defend against Ruy.

Developing pawns isn't as important as developing pieces, while you develop the pawns, you create queenside weaknesses that your opponent can try to use against you.
which weaknesses? how to exploit them?
CallMeMisha shows a game in which this is a good move, what are the differences?
The weaknesses created with an early c7-c5 advance are all of the queenside pawns.
4... b5 is the third most common continuation, however it is few in comparison with the usual 4... Nf6 or 0-0 games.
After 4... b5 the obvious weaknesses are the backward a6 pawn, which is defending b5. B5 can be attacked via a2-a4, creating a problem along the a-file because of the undefended rook on a8. C7 is backwards as well. With the white bishop on b3 it tempts black to play Na5, thus creating another problem for black if white plays a4 immediately and offers the exchange on b3 then c2xb3 will give white the open c file against the pawn.
Of course these are weaknesses in all the games however not so easily exposed because black develops the pieces first in order to aid the pawns and influence the center.
I just played a game in this variation and black played b5 early as well.
... I must learn how to defend against Ruy.
Possibly helpful:
A Spanish Repertoire for Black by Mihail Marin (2007)
https://web.archive.org/web/20140626195205/http://www.chesscafe.com/text/hansen102.pdf
http://www.qualitychess.co.uk/ebooks/SpanishUpdate.pdf
The Berlin Defence by Igor Lysyj & Roman Ovetchkin (2012)
https://web.archive.org/web/20140627104938/http://www.chesscafe.com/text/hansen159.pdf
http://www.chess-stars.com/resources/contents_Berlin.pdf
The Ruy Lopez: A Guide for Black by Sverre Johnsen and Leif Johannessen (2007)
https://web.archive.org/web/20140627023224/http://www.chesscafe.com/text/hansen94.pdf
http://www.gambitbooks.com/pdfs/The_Ruy_Lopez_a_Guide_for_Black.pdf
Bologan's Ruy Lopez for Black by Victor Bologan (2015)
http://www.sjakkbutikken.no/produkter/bologans-ruy-lopez-for-black/
https://www.newinchess.com/Shop/Images/Pdfs/9016.pdf
Starting Out: Ruy Lopez by John Shaw (2003)
https://web.archive.org/web/20140627024240/http://www.chesscafe.com/text/hansen53.pdf
Play 1 e4 e5! by Nigel Davies (2006)
https://web.archive.org/web/20140626201436/http://www.chesscafe.com/text/hansen80.pdf
https://web.archive.org/web/20140627083715/http://www.chesscafe.com/text/hansen98.pdf
The Kaufman Repertoire for Black & White by Larry Kaufman (2012)
https://web.archive.org/web/20140626221508/http://www.chesscafe.com/text/hansen162.pdf
https://www.newinchess.com/Shop/Images/Pdfs/955.pdf
The Berlin Wall by John Cox (2008)
https://web.archive.org/web/20140627050257/http://www.chesscafe.com/text/hansen115.pdf
http://www.qualitychess.co.uk/ebooks/TheBerlinWallInternetexcerpt.pdf
Attacking the Spanish by Sabino Brunello (2009)
https://web.archive.org/web/20140627105306/http://www.chesscafe.com/text/hansen124.pdf
http://www.qualitychess.co.uk/ebooks/Attacking_the_Spanish_excerpt.pdf
The Ruy Lopez Revisited by Ivan Sokolov (2009)
http://dev.jeremysilman.com/shop/pc/Ruy-Lopez-Revisited-The-p3765.htm
https://www.newinchess.com/Shop/Images/Pdfs/931.pdf
Fighting the Ruy Lopez by Milos Pavlovic (2009)
https://web.archive.org/web/20140627105306/http://www.chesscafe.com/text/hansen124.pdf
Slay the Spanish by Timothy Taylor (2011)
https://web.archive.org/web/20140627040230/http://www.chesscafe.com/text/hansen146.pdf
Grandmaster Repertoire 13 – The Open Spanish by V. Mikhalevski (2013)
http://reviews.dailychess.org/grandmaster-repertoire-13-the-open-spanish-qualitychess-by-v-mikhalevski/
https://www.newinchess.com/Shop/Images/Pdfs/7234.pdf
Anti-Spanish. The Cozio Defence by Alexey Dreev (2014)
http://www.chess-stars.com/resources/contents_Cozio.pdf
Playing 1.e4 e5 - A Classical Repertoire by Nikolaos Ntirlis (2016)
http://www.qualitychess.co.uk/ebooks/Playing1e4e5-excerpt.pdf
The Spanish Main Road by Evgeny Solozhenkin (2016)
https://www.newinchess.com/Shop/Images/Pdfs/7595.pdf
The Zaitsev System by Alexey Kuzmin
https://www.newinchess.com/Shop/Images/Pdfs/9036.pdf
That's a really good extensive list that you have. Don't you have a day job or something to be working on?

Maybe kindaspongey is an organized guy who maintains lists. Who knows. But it's nice of him to share his knowledge, assuming he did more than google Ruy Lopez and splat out a buncha links which turned up.
I played the Black Ruy for a while and liked the games from it. There is a real classical beauty to the Ruy for both White and Black. The main problem IMO was that White was equally likely to head off into some Giouco Piano/Scotch Game/King's Gambit/Whatever which I didn't like and didn't want to learn.

Oh. It would be a shame if he had just done that. GOOGLE IS HIS FRIEND. AND SCRIPTS FULFILL HIS SOUL.

Maybe kindaspongey is an organized guy who maintains lists. Who knows. But it's nice of him to share his knowledge, assuming he did more than google Ruy Lopez and splat out a buncha links which turned up.
I played the Black Ruy for a while and liked the games from it. There is a real classical beauty to the Ruy for both White and Black. The main problem IMO was that White was equally likely to head off into some Giouco Piano/Scotch Game/King's Gambit/Whatever which I didn't like and didn't want to learn.
You might like this repertoire idea: http://www.kenilworthchessclub.org/games/java/2009/open-g6-pt1.htm
http://www.kenilworthchessclub.org/games/java/2009/open-g6-pt2.htm
It leads to positions that tend to avoid the early tactics in the open games.

penandpaper: Interesting. I knew of the the g6 fianchetto Smyslov played against the Ruy, but not a general double king-pawn system based upon it. Sounds like a good change-up for blitz.
I don't mind tactics or study. There's something about double-KP openings, except for the Ruy and King's Gambit, which puts me to sleep.
After 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 chessmasterssays that the best move is 4. Ba4 and not the exchange. okay i can understand this, but i can't understand why next black move isn't 4. ... b5, because white must once again move his bishop in the opening and black has developed queen side pawns. Chessmaster suggests 4. ... Nf6.