The word "minimum" means "the least amount". You can use it like this:
You know, a lot of people just try to do the minimum amount of work that they can get away with.
The minimum age is 18.
Some stores have a credit card minimum. This is the smallest amount of money that you can use a credit card to pay for. For example, if you try to buy something that costs $5 but the store has a "$10 minimum", they will ask you to pay with cash instead.