A mail services center is a place where people can go to send and receive letters and packages. It's kind of like a big post office, but usually it's located in a building or on a college campus.
When you go to a mail services center, you'll usually see a counter where a person called a clerk will help you. They'll ask you what you want to do - whether you're sending something, picking up a package, or just buying stamps.
If you're sending something, the clerk will ask you how much it weighs and where you want it to go. They'll weigh it on a special scale and then calculate the cost. Usually, you'll have to pay for postage by buying stamps or using a credit card. Once you've paid, the clerk will put a special label called a postage stamp on the letter or package.
If you're picking up a package, you'll usually have to show some kind of identification to prove that it's yours. Then the clerk will go to a special room where all the packages are stored, and look for your package. Once they find it, they'll give it to you to take home.
The mail services center is a really important place because it helps people stay in touch with each other. Without the mail services center, it would be really hard to send letters and packages to people who live far away.