Open cinema forge.
There are 3 type boxes (as in boxes you can type in ^^).
Click on the button next to the 1st box (looks like some film) and select the file.
Ignore the 2nd box - thats for putting different sound over a video
When you select something in the 1st box something should appear in the 3rd box. This is where the new file is going to go.
Next to the third box there is a little button that says "Doc Type" click this and select what format you want from the drop down list.
Click the "Encode" button.
Your file will be saved to the same folder that the original file is in.
Other stuff: - you dont have to do
Turn off thumbnails on the side options. For every video you create it will make a thumbnail otherwise O.o
Change output video quality & size (I dont bother, plus you can make a video better quality than it already is)
If you open cinemaforge and there's a big blue box covering half the window just close it and open it again, it'll go eventualy.