Most people learn Photoshop to use with the mouse but after some long nights and some sore wrists, you'll want to do it a different way. Then you have two choices: get yourself a wacom tablet and a pen or learn the shortcuts by memory. If you decide to do the last, you will really master Photoshop. So then maybe you can make some money off it and get the tablet after all.
But be warned: when you know the shortcuts you're work will be done faster and easier so you might end up spending more time with your family/children/boss.