Help with shipping?

Help with shipping?

I’m still fairly new and I’m trying to figure out shipping. I want to do ‘snail’ mail. I make stickers and all of my packs are under 1oz. I need help with envelopes and postage, is it too bad of a thing to do to charge for shipping? How do I include the postage? Do I need to include a return address? I don’t have a p.o. Bx. Can I still use snail to send a letter to canada? I’m in the US.