i need a couple of paragraphs on the information below

Certificates are used all the time in computer networks and the Internet. Think of them like a driver’s license or other form of ID that a person might carry with them. Let’s say you have installed on one of your servers, the CA to issue them to computers in your company. After a while, you notice that an error will come up from time to time on machines in your network saying the certificate is invalid when doing work on the Internet.

What are some possibilities that might cause errors like that? Where can you go to check a computer’s certificate? Does the certificate need to be updated? Is the error message in fact coming from your computer (and network) or perhaps it’s the computer you are connecting to on the other end?