For all you just starting out on Photoshop, or are looking for the four most useful brushes ever with no confusion, just download this pack
It comes with a sketch brush, a inking brush, a flat brush, and a shading brush. I use these brushes 100% of the time in every work I do. I use some more, but they're not as reliable as these are.
To install just download and double click the pack, and they should appear in you brush cue at the end.
If you have any questions, please ask :3 other resources