It will very much depend on the type of work you intend to do. If you are going to be 1st fixing or shuttering, a circular saw and hammer drill are essential. A nail gun is very useful but a luxury if just starting out. If you intend to carry out 2nd fix then you will need battery drills, routers, chop saw and jig saw as esential and if fitting kitchens you will need jigs for jointing worktops. Start buying the basics first and then see what type of work you are getting and purchase more specialist tools when you need them. Buy the best you can afford as cheap tools are ok for DIY but do not stand up to being abused on a daily basis. To get experience, you could offer to help a tradesman in exchange for being shown and having the chance to watch and learn. Good luck as it is a great trade!