How do i play mp4 and mpg files

Question

Hi all Can any fellow experts help me with this problem as computers isnt my area of expertise can you please tell me how i play files that i download from limewire i can play music files no problem but when it comes to video files i cant play them, i think maybe i need the sofware if so what software do i need to be able to play this im hoping their are plenty of free ones out their for me to download.Many thanks in advance