Freezing breast milk?

Hey, I'm a ftm and I'm in the third trimester. I plan to exclusively breastfeed unless I can't for some reason. I've seen a lot of people recommend freezing breast milk in bags and will probably try to do this myself.

What is the process you use to do this? Any extra milk you pump you pour in the bag, then freeze? Then is there a particular way you have to warm it up when you want to use it? Can you sterlise and reuse bags or are they one use? How long can you keep the milk frozen for?

Sorry, I have no idea what I'm doing with breastfeeding, this is all new to me. Any advice would be appreciated!