Sony Ericsson W600i / W550i

Hello, i am new to this forum 😕 .I am trying to play videos on my W550i.I cant seem to be able to play them.I have tryed .mp4 format and .3gp.1=Were shall i put the videos on my mobilephone..2=What format. I would highly appreciate it if you could help me.
Thanks. 😎