Help with Python version

I installed Python (3.9.1) on a Mac but I have a default version installed (2.7.16) when I search Python version on the terminal it apear 2.7.16 but if I look Python3.9 the version it’s 3.9.1 does it affect to have both versions?

If someone can help me I would really appreciate it

Your question is not entirely clear.

Mac and Linux have a system python already installed. That must be there to run your system. Try not to make changes to it, especially if you’re unfamiliar with it.

The Python3.9 version you installed is a separate python. It’s common to have both on a system, but you should use the Python3.9 version. This means you should be careful when typing python vs. python3 (or python39, etc.).