I know the openings, but when to use them?

But then, noone sane enough would want to achieve your kind of "improvement".

So is there anything other then tactic trainer to become better at our levels? Is positional chess knowledge wasted for the u2000 player?

I want to become better, I asked in my chess club yesterday and I got the following advice: play a lot of internet chess and....know your openings! But I must say most people on my chess club are older then 60 years and they know their openings well! But just as mr. pfren said openings are overrated.

Because it's true that tactics determine most of the chess games u2000. Most if not all my games on the chess club have been decided by tactics.

Tactics decide almost every game at any level.  Just because there is positional play going on doesn't mean there aren't tactics going on as well.  They are there behind the scenes at every turn -- I'm making this "positional" move, but if you reply wrongly, boom, I uncork this tactic against you.  

And I don't know why people think endgames aren't tactical -- they are.

I would only use the openings at the beginning of the game. It could be awkward otherwise.