Yongnuo yn-560 ii with a d3100?

I'd like to know if this flash is compatible with the Nikon d3100! I know it's a manual flash but will I be able to mount it on the hot shoe on the camera and use it?

It probably can work, but I wouldn't count on it working well. Money spent on something cheap sets you that much further back from saving for something good. Wait until you can afford a Nikon SB700 and be actually happy with it.

It will work but you'll have to do everything manually (Exposure etc)
If you get a Nikon dedicated flash, you can set the camera on Auto and it will calculate correct exposure and flash output for you.

Yes.

http://keerok-photography.blogspot.com/2012/08/how-to-use-generic-flash.html