Its about samsung star 2 phone...pls jus help me out...?

hey guys i jus brought this cell phone.. i transferred al d files but then the video's arent supporting n hence it isn't playing.. should i download any software to convert those video files so dat it'l play in my cel>? if anyone knows it pls let me knw.. n can u guys tel me as to where do i download themes for d same cel? thanks a lot for spending ur time :)