An enterprise portal is like a magical door that takes you to a special place where you can find all the important information you need to do your job. This is like a secret clubhouse that only the members of a company can access.
Imagine you are going to school, and you need to know when your classes start, who your teacher is, which books you need, and what homework you have to do. You could go to each teacher and ask them, or you could go to the school office and look at a sheet of paper with all the information for your classes.
An enterprise portal is like that sheet of paper, but for work. It might have information like your work schedule, your company's policies and procedures, your benefits, or the projects you are working on. Instead of having to ask your boss or coworkers for this information every time, you can just find it all in one place.
Sometimes there are other fun things on an enterprise portal, like a directory of all the people who work at the company, or a forum where you can share ideas or ask for help.
Of course, not everyone can get into the enterprise portal. You need to have a secret code, like a username and password, to be able to use it. And just like your parents tell you not to share your toys with everyone, your boss will tell you not to share your enterprise portal information with people who don't work at the company.