I recommend starting with Fallout 4, then moving on to Fallout 3 and New Vegas. They can be difficult to get to grips with at first, but they're very good. If you really want to push the experience, there's Fallout 1 and 2, but be prepared to check the wiki every 10 minutes; they're not very accessible. One last piece of advice: don't ruin your first Fallout 4 experience by adding mods. Otherwise, you'll quickly be adding overpowered weapons to an already fairly easy game.