you pay for an account on some server. that helps the server with bandwidth and storage costs. the server you use knows where some popular forums are (sort of like fediverse) and will cache certain boards.
when you want one of the items, you ask your server for it and they shove it down the pipe.
don’t forget to pay your bill.
edit: i only read the title. it seems like i literally taught you nothing. sorry to waste ur time.