changing brightness of a selected area

Lately, I've found exposure adjustment particularly useful for this kind of work. It can be used on its own or combined with other adjustments as needed.

Is the original a raw file or rendered such as a JPEG?

If the latter, copy the selection to a new layer and then try the shadow/highlight command.

mwfast  wrote I have a photo with a very bright, over exposed hand. I have selected it with the lasso tool. How do I adjust the exposure/brightness on just this area?

I have a feeling that you'll find you do not get a good result with the adjustment layer. If that is the case, copy the image and paste it to this thread, and we'll show you the best way to fix it if possible.  The bottom line tends to be that a blown pixel will always be a blown pixel, and you can't detail back, but there are a few tricks you can often use.

Click on the layer mask icon in the layer panel and select one of the following :

1- brightness and contrast

2- Levels

3- curves

then adjust the values