Salary Cap Explanation

Sorry for this silly question but I can´t trade anyplayer because I get the same text "clear up some salary cap" (or something like that) what this mean. Please explain me how to trade players. If you know post it and let me know
Thanks
Anubis AK

I think what you want to know is you can't go way more over the salary cap. Add up the total salaries for the players you are trading on each team. The trade can happen if the numbers are very close.