How to select movie recording mode in nikon d3100?

This sounds silly but i can't really find the mode on my D3100… Bought it this evening

You press the little button with the red dot on it above where it sais Lv on the back of the camera (Lv stands for live view which is accessed by sliding the little thing clockwise then releasing it).

Do you have an instruction manual? Read it! If not go to the Nikon site. There you can download a pdf version of the manual.