What does this command do?
export PATH=/usr/bin:$PATH
This command adds /usr/bin to the beginning of your PATH environment variable.
What is PATH?
PATH is an environment variable that tells your shell (like Bash or Zsh) where to look for programs when you type a command:
Your system looks through all the folders listed in PATH, in order, to find the python program.
What does /usr/bin:$PATH mean?
Why use this?
Sometimes you want to make sure a specific version of a program (like one in /usr/bin) runs before others. Putting /usr/bin at the beginning gives it priority.
Summary
The command ensures that when you run a command, your system will look in /usr/bin first before checking other locations in the PATH.