How to Pass Ubuntu PATH

I installed python 3 series on Ubuntu, but
I just don't know how to use PATH.

https://qiita.com/takanemu/items/6027291be8a2a6af9adc or
https://www.motokis-brain.com/article/122
I am also looking at the website, but in my case, I do not know what to add.

In the case of the display results below, where and what should I add to pass the python3 PATH?

#echo$PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# which python 3
/usr/bin/python3