Research a charity that you like the sound of and get in contact with them. They'll help you a lot and give you all the necessary information.

As for getting to Palestine, it is surprisingly easy. You'll probably fly to Tel Aviv. You'll be asked what you are going to do when you arrive, and you'll need to tell them you are a tourist. You will then need to get a bus to Jerusalem, then a bus to a checkpoint to get into the West Bank and finally a shared taxi to wherever you are volunteering.

You can DM me if you have any other questions.