[arriplify]

For floating currencies, they are bought and sold at market like stocks, give or take, either individually or more commonly as "baskets" of currencies ("SE asian currencies", ie).

Currencies can also be "pegged" to another currency, for example the Bolivar is "fixed" at 2.15/$ or whatever the other thread mentioned. From my understanding, that usually means that the Venezuelan National Bank will give you $1 for every B2.15 you hand them, guaranteed regardless of the real exchange rate. In some cases this works this way; in some cases it's a theory that is not so effective in practice (ie, they won't really give you that amount).

Pre-WWII, many currencies were pegged to the Pound; this played a significant role in the Great Depression, because when a few Pound-pegged currencies were hit, it affected all of the Pound Sterling pegged currencies.