You lock coins you already hold behind an answer. Nothing is bought, nothing is sold, and you get them back.
A lock is an amount of your own BSV that you put behind one answer, Yes or No, until a set moment. You choose the side, and you choose the amount: anything from the proposal’s minimum up to everything spendable in your wallet.
The coins stay yours the whole time. They are frozen, not spent. Nobody can take them, nobody else can touch them, and when the time is up you have every satoshi back, whichever way the question went.
The shortest lock runs until the proposal closes, and there is no way out early. That is the point. If you could pull your coins back the moment an argument turned against you, locking would prove nothing about what you actually think.
That is the whole mechanic
Everything else on this site is a way of looking at those numbers.