First I don't know why you installed Python. macOS includes a version of Python. Unless you needed a different version, you should not need to install Python.
"Add python installation folder to system PATH."
A folder (directory) created when you installed Python contains executables. You modify the PATH environment variable to tell the Unix side of macOS where to look for executable commands when you type a command at the Terminal command line prompt.
The default PATH tends to look something like
export PATH=/usr/bin:/bin
It is a colon separate list of directories (folders) to search when looking for executable commands
You can use the command
printenv PATH
to see what your PATH currently look like
You would modify PATH by adding a colon and the full path name to the Python directory they want you to add to PATH
export PATH=$PATH:/the/full/path/to/the/python/directory
No spaces except between 'export' and 'PATH'
$PATH provides the current setting for PATH, so you do not need to enter it yourself, and you will get all your existing PATH values.
NOTE: If you mess up PATH, you will start to get errors says command not found. So be very careful when changing PATH.
If you want this PATH change to be there they next time you start a Terminal session, you need to put the
export PATH=$PATH:/the/full/path/to/the/python/directory
Into .bash_profile in your home directory. This must be created with a text editor, NOT a word processor!
nano .bash_profile
is an acceptable choice