Mina is a unit of measurement that people used to use to measure things like grains and gold. It's kind of like using a ruler to measure how long something is, except you're using the mina to measure how much of something there is.
Think about it like this: let's say you have a bag of marbles, and you want to know how many marbles are in the bag. So, you take your mina and pour the marbles into it. If all the marbles fit inside the mina, then you know you have one mina's worth of marbles. If there are still marbles left outside of the mina, then you know you have more than one mina's worth of marbles.
Mina is a little different from other measurement units because it can mean different things depending on what you're measuring. For example, one mina of gold might weigh a lot less than one mina of flour because gold is more dense (meaning it takes up less space for the same amount of weight) than flour.
So basically, mina is a way of measuring how much of something there is. It works kind of like a ruler, but instead of measuring length, it measures weight or amount.