Think of it as a bar tab: you hand the bartender your card once (the channel-opening transaction), order all night with zero friction (off-chain payments), and settle a single final bill at close (the channel-closing transaction). Between open and close, the two parties can shuffle the locked balance between themselves thousands of times per second, for fractions of a cent.
Payment channels are the atoms of the
Lightning Network: chain enough of them together and a payment can hop from you to anyone on the network through intermediary
nodes, without you opening a channel to every counterparty.
Public channels are announced to the network for routing;
private channels (common between wallets and their service providers) stay invisible — one reason public capacity statistics understate the network's real size.