Contrast is, of course, the difference between the brightest bright and the darkest dark in your video.
Brightness raises or lowers the white or black levels of your video.
Exposure raises the overall video gain.
There is no set method for brightening a video. Most likely your best results will be a combination of these settings -- but only trial and error will tell you what the combo is.
Steve, thanks for your reply.
I understand the different methods can all brighten my clips. What I don't understand is what the difference is between exposure, brightness & whites sliders, ie how they work to brighten the image.
Have you seen Adobe's description on its effects?
If not, please review and consider
Brightness and Contrast description on an Adjust category
Black Clip and White Clip under a Shadow & Highlights category.
I suspect that these are generalized descriptions that transcend Premiere Elements version.