How to format songs and what format do i change it to, in order to listen to it on my cell phone.

because

i put songs on my sd card but when i put the card in my phone, it says player error or when i go through my music and go to play all to start song list play it says music not avaliable and player error pops up again, someone please help, i really wanna put music on my cell phone. Because there is music on my card but they dont show up and play on my phone.;(
help????

Electronics - Others - PNY - 2GB microSD Memory Card