How can i make reverse video?

Question

for free. a already have a camera

Answer 1

most video editors have a "special effect" that will do this. At least, iMovie (in Macintoshes) lets you do that... If you are running Windows, you can check to see if MovieMaker does it.

Since you didn't tell us what camera - we can't tell you how to connect the camera to the computer to transfer the video.