I use a Nikon D60 SLR camera, but I can't use a soft box. What is the button behind it for?

I think you are involved in several different issues.

1 What is a soft box? A soft box is a box that can soften light. It is an accessory, and it is useless by itself. ...

There is a button at the back: I guess you mean flashing lights! The flash used in the studio is generally used in conjunction with the soft box. The buttons at the back are generally power switch, flash switch, modeling light switch, voice switch, output intensity and pre-flash.

3D60 should be used with flash, using # flash # or # flash extension line #. Synchronize the camera with the flash.

I hope it works for you. Please refer to keywords for details.