Nikon d3100 video mode?

Hello guys - I'm posting another question. I'm buying my first DSLR. I just wan you to tell me how is the video mode like on the D3100? I know it is continuous autofocus. That to me sounds really irritating - like focuses again n again!
Will it be able to just shoot videos like you do with a mobile camera, just press a button And voila everybody and everything is in focus? Can't DSLRS do tht?
Sorry if this is a really stupid question to you guys, As I said this will be my first dslr

Not a stupid question. DSLR's that used to shoot video don't have autofocus.so.you'd have to manually focus the lens while shooting. This is an okay option, but continuous autofocus will improve upon it. It's just like camera autofocus and will intelligently sense a subject to focus on. (eg. If a person moves closer it'll "lock" focus on the person) before, the photographer would need to adjust focus on the lens while the person is moving closer.

the D3100 is a good choice, and i'm glad you've decided to upgrade to a DSLR.