Well kiddo, do you know what an excuse is? It's when you make up a reason for doing something, right? Well, pretext is similar. It means that you make up a reason or an excuse to do something that might not be allowed, or might be frowned upon.
For example, let's say you didn't do your homework, but you really want to play video games. You might say to your mom "Mom, I need to use the computer for my homework," even though you really just want to play games. That's a pretext!
Sometimes people use pretexts to avoid getting in trouble, or to get what they want. But it's not always a good idea. It's better to be honest and upfront about your intentions. So always remember to be honest, even if it's easier to make up excuses or pretexts.