A subject access point is like a signpost that shows you where to find certain information in a big book or on the internet. It tells you what the information is about and where to find it.
For example, if you wanted to find all the information about dogs in a big book, you could look for the subject access point "Dogs" at the beginning. It would tell you which pages to look at to find all the information about dogs in the book.
In the same way, on the internet, you can use subject access points to help you find information. When you type something into a search box, the subject access points will help you to find exactly what you are looking for by showing you the most relevant websites and pages.
So, think of a subject access point like a map that helps you find what you want in a big and confusing place like a book or the internet.