What is the FBML tag or any other option (I mean in API) to take photo from a webcam in Facebook (and next upload it to my profile)? I can see such an option in my profile, but I don't know how to use it in Facebook app.
There is no such option (as far as I know). In any case FBML will be deprecated on June 6, 2012. You will have to look into the video API https://developers.facebook.com/docs/reference/api/user/#videos.
There are examples on the Facebook Developers' blog of how to achieve this