I don't understand the Scandinavian Defence

To my knowledge, the best Black can hope for is losing a tempo:

1. e4 d5 2. exd5 Nf6 followed by c6 and Nxc6 or cxd5 if white declines the c6 pawn was a line I used to play in blitz and especially bullet. Personally, I don't look at the Scandinavian as a viable defense outside of the club scene, though plenty of masters do use it.

To your op, though, black does lose a tempo in bringing the queen out so early, but if you study the theory, it's a fairly solid defense even though white has an advantage in development. Again, it's not one I particularly like or use anymore, but to each his own. Lots of folks swear by it. Try the Modern if you don't like the Scandinavian, or even the "Sniper", which is a pseudo-Sicilian, minus so much theory. Both are pretty flexible and the Modern can transpose into a King's Indian so, if you like it, it can be a solid defense against e4, d4 or c4.

Losing a tempo might not be such a big deal, as Nc3 stands in front of the c2 pawn which might be better placed on c4. Also Black gets a solid, easy to play position. Surely not the most ambitious opening in the world, but  pretty decent at club level.

Play me I like it.

The modern treatment with kn f6 is better

White loses a single tempo capturing the pawn, Black loses a single tempo taking back the material, and White makes Black lose tempo while developing his knight.

@iamunknown2

Black does NOT lose a tempo recapturing the pawn, because he does it in one move.  He actually GAINS a tempo, because if you look at the position after move 2, Black has the only developed piece in the game.  True, it's his Queen and thus not ideal, but it's still a tempo.  White then wins the tempo back with Nc3, and after the Queen moves somewhere, both sides have one piece developed.  The tempo count is even, though White still has his advantage of the first move.

Suppose instead the following (hypothetical) move order happened.  Obviously it's ridiculous, but it shows the difference in tempo clearly.

Of course black loses time in the Scandinavian. If he didn't, it would be the refutation of 1.e4. As usual it comes down to a trade-off: In exchange for his loss of time, black gets the desirable d7-d5 advance without any preparation move like in the French or Caro-Kann, and as a result white cannot close the position with e4-e5 like in the French or Caro-Kann.

I consider 1....d5 is the worst common reply to 1.e4. Never play that and hardly lose a game when I play white against a same rate player.

I think there are a few things black gets in the Scandinavian. 1. Black steers to game into his territory 2. Black often gets a very solid structure with pawns on c6 and e6 3. White might not be well prepared against this somewhat rare opening and might try a little too hard to prove that he's better.

interesting.. 

3.Nf3 instead of 3.Nc3

Kick his queen with your pawns (pawn duo on c4 and d4)

I have good results with this idea.

Join the 3...Qd6 or the 2...Nf6 Scandinavian Club at Chess.com. These are probably the most active clubs for this Defense. 

I think the third option is the best!😀

One continuation I've often seen is 1. e4 d5 2. exd5 e6 3. dxe6 Bxe6, which leads to this:

Black has a clear development advantage and an open center (which will begin to look dangerous after 4. ..Bd3), at the price of allowing white to firmly consolidate the gambit pawn.  Seems to work OK against A- and B-rank players, though some might consider the compensation a bit light for the gambit pawn.

"The idea behind the Modern Variation is to give back the pawn in order to achieve quick development.

As usual SM is talking out of his Btm.

"

1. e4 d4 2. exd4 Nf6 is the modern variation, works well, and gains a tempo.

1 e4 d5 2 exd5 Nf6 without loosing tempo

Yes, in the mainline, black temporarily loses a tempo after white develops with Nc3.

But it also coerces white into blocking his c-pawn with his knight. So there's a positional trade-off. Now white can't immediately establish a centralized pawn duo with c4+d4.

And, if white ever wants to move that c-pawn, he'll have to relocate the c3 knight—thus giving the tempo back.