Can someone help me understand the Scandinavian Defense?

I don't really understand the point of this opening, why would black bring out the queen too early and let it be attacked with Nc3? Why would black want to move his queen twice? I would like to understand the reason that many people like to play the Scandinavian Defense as black.

As with all openings the Scandinavian Defense it has its drawbacks and is not for everyone, but if you know how to play it well you can win games with it.

There's nothing wrong with the Scandinavian Defense. I don't play it, but that's because I find the typical Scandinavian lines boring, not because I consider it unsound.

You feel that Black loses a tempo by allowing his Queen to be attacked?

Excuse me... can we just count moves?

You also don't have to re-take with the queen right away. I like to play nf6 and most people will walk into this

and black's queen is allowed to remain in the center with little resistance

But then black loses TWO moves by moving the queen back and forth. Just look at this:

White has 2 knights out already

Why Qd8? You do realize that Qa5 is literally TEN times as common? Qd8 is a rare side-line.

tell me why it's a book move and why many people recommend it

It's a book move only in the sense that 1. e4 e5 2. Nf3 f6 is a book move.

3. ... Qa5 is played ten times as often... five times as often if you count only Master games.

In those cases, it's played as a Hypermodern system, similar in principle to the Gruenfeld.

But to describe it as "popular" would be fatuous.

Just because it's a book move doesn't mean it's good. There's a sicilian variation where white blunders a knight by blocking the queen with a bishop. It's still considered a book move, but is it good? No. I'd suspect the reason people recommend going back is because it's much safer than Qa5. Qa5 puts the queen in an area where it can't really be attacked, and is at least a little active. But going back does indeed lose time, and doesn't seem all that great to me.

But many people recommend it, and GothamChess says that John Bartholomew plays it too 

Move count is only a small part of the equation. Even after the …Qd8 move, white still has to show that black can’t just go Nf6, Bf5, Nbd7, e6,c6, (in some order) move the Bf8 and 0-0 etc and be totally fine. If white simply plays insipid development the ‘extra’ moves that may seem apparent after move 3 will not be noticeable if black is able to set up ideally without being disturbed. 

My favorite example:

All book. This line has been played hundreds of times, by players up to GM strength.

White has won 36% of the games, with 21% drawn and the remaining 43% won by Black.

Advantage Black... right?

Or maybe not.

How's Qd7? I know it's a line, but is it just bad because it blocks the bishop?

And also because Ne5 is a thematic move for White in the Scandi ANYWAY... putting the Queen on d7 just gives it extra force.

- Take the initiative

- Unbalance the position

- Psychological pressure on the opponent

- speedy development of queenside

Yeah, that's what I thought. It blocks development and is a square which can be easily targeted.

I think in  this line the Black queen is too exposed. It may even be a loss for Black

suggest stay away from this particular line.

?

Sure, but after Qxc3 Black is down in tempo just as surely as if he had allowed his Queen to get chased around. The move 2. ... Nf6 doesn't solve all of Black's opening problems.