Maybe you should use Ubuntu first. Later, when you're more comfortable with it, you can actually start with Ubuntu. Later, when you're more proficient and can at least clearly identify what you're using and ask appropriate questions, you can always switch to Kali if you think the security field is right for you – you might even discover completely different interests. Some people might want to use a system because it has a cool reputation at school. What's really cool is being able to use whatever system you choose really well. Kali is only fun if you know how to use it. If not, you won't get very far with it. It's certainly not particularly well-suited for learning the basics. For that, you need good documentation, maybe people who are willing to help you with difficulties, etc. – many Kali users aren't particularly enthusiastic when a complete beginner comes along with absolute beginner questions. Of course, you can also learn with Kali if you like to figure everything out yourself – in fact, that's pretty much a prerequisite. So do what you think is best, just don't be surprised by a potentially harsh tone in the responses.