You really can make stuff with used plastic milk jugs, and it’s not hard. Just cut them open so you can clean them thoroughly inside and out (or else you will get burnt brown spots) and heat them up to 350 deg F. I don’t encourage experimenting with any other plastics unless you really know what you are doing because they can emit poisonous fumes when heated, but if you see the number 2 in a triangle (like in the screenshot) and stick to 350 degrees then you’re probably OK.