It’s a way to trade – to buy and sell things – without official currency.
Mortgages, savings accounts and (sometimes) current accounts; owned by their members.
Currencies (like Bitcoin, for example) controlled by blockchain technology, not corporate banks.
Local / independent currencies
Use currencies that stay in your local community, instead of being sucked out by corporate branches.
Invest in land co-ops, community energy etc. for a better return than from a bank savings account.
Local co-operative savings & loan schemes: an alternative to loan sharks.