Don't get an openings book. If you're failing at tactics, practice them.

http://www.chesstactics.org/ and practice on this site.

But study endgame. Firstly, make sure you know how to mate with 2 queens, 2 rooks, 1 queen, 1 rook, 2 bishops. Then do pawn endings, rule of opposition, king activity etc.

Learning an opening barely teaches you anything at a low level. The principles are enough.

Does it cost to do the tactics on this site?

You can only do a few free I think. Check your messages.

Here is a youtube video witch explains chess notation very well.

http://www.youtube.com/watch?v=Utur_MVjba0

Understanding chess notation isn't necessary to just play but if you want to get better it is well worth a few minutes to learn it.

http://en.wikipedia.org/wiki/Algebraic_notation_(chess)