When you open a RAW image in Photoshop you get the display shown below. In this case the image is quite badly under-exposed
(one of my early shots from 2005, honest!) and hence much darker than I want it to be.
The first thing you can try is to click 'Auto' to see what Photoshop thinks will be the best adjustments for your image. I nearly
always try this but seldom accept the auto settings.
So here is the 'Auto' modified image.
In this case I think it has made the image too bright and so loses some of the detail. I corrected this by restoring the original
image (simply by clicking 'Default') and then using the 'exposure' slider to increase the exposure by +1.5 stops, then using the
'brightness' slider to increase the brightness to +60 and then using the 'shadow' slider to reduce the shadow value to zero. This
creates a much more pleasing picture in my opinion. It still needs some work but the exposure is much better.
If necessary (or if you feel like it) you can also experiment with the other sliders to increase or decrease the contrast and/or the
colour saturation. You can't do any harm so long as you don't save it and you can click 'Default' at any time to restore the original
settings.