And when you say: "I play football", its "gram w pilke nozno". why is there an "w"?
all the games require the 'w' preposition:
gram w karty - I play cards
gram w brydża - I play bridge
gram w berka -
gram w siatkówkę - I play volleyball
gram w tenisa - I play tennis
the reason that games require the preposition might be this:
gram has also a meaning of I pretend(I play, I act like) but also I play (a role) - which are quite near semanticly
so there is: gram wariata/gra wariata - I play an idiot/looney (like to play dead), zgrywam (zgrywam is derivate of gram) głupiego, zgrywam durnia - I play stupid
grać/zgrywać wariata is colloquial for to pretend one doesn't no about something in question
there is also the meaning of grać which is connected with music
grać Szopena - to play Chopin, grać Beethovena, grać mazurki (play masurkas), grać wesołe nutki - to play merry tunes
a contrasting pair can be formed for example
grać w piłkę - grać piłkę
grać w piłkę - means to play some ball game (but usually means football - czyli w piłkę nożną)
grać piłkę means however to play a ball - say in a weird form of acting/performance
I can't explain to you the origins of the 'w' preposition here - but it does play some role in distinguishing meanings (disambiguation means) as you can see (czyli gra konkretną/określoną rolę w odróżnieniu znaczeń ;) )
there is more to tell about that but I think it is enough of a lecture already :)