Someone who is "cheap" is a person that is reluctant to spend money. It's a negative way to describe a person.
Some people are reluctant to spend money and can be called "cautious", that is a more positive way to describe a person. For example, you have bills to pay so decide to cook instead of going to a restaurant. This is positive because it's responsible to be careful with your money.
A "cheap person" is a person that is ungenerous with their money.
For example, I want a pair of $50 Nike shoes, but my mom buys me FAKE Nike shoes that cost $15. Yes, the fake Nikes are cheaper, but their quality is poor. Most people would prefer paying the extra money for the Nikes because they are of higher quality and will last longer, but my mother doesn't care about that. My mother is cheap because the only thing that matters to her is to spend as little money as possible.
Someone can be rich, but be cheap. For example, billionaire Donald Trump buying his wife a Ford when she preferred (and he can afford) a BMW.