Beginner Question

I'm just a beginner.

Assuming I open with white to K4 and my opponent moves to Q5, what is that variation called and what is my best response?

Thats the center counter game I believe, you normaly would take, black responds with Qxd5, and then you respond with Nc3 attacking the Queen and keeping tempo

Also popular is 1. e4 d5; 2. exd5 Nf6

and a typical continuation would be 3. d4 Nxd5

That's the Scandinavian Defense. When played at top level play usually continues with 2.exd5 Qxd5 3.Nc3 Qa5 .

Just try a few different moves and you will find out .

Everyone is correct! What a great group of people!  I did a quick search of chess.com and found this interesting article.  You might try a search of your own and see what you can find.

http://www.chess.com/chessopedia/view/scandinavian-defense

Good luck.

Thanks everyone