To run a python script there are two approaches.
Suppose the script is called script.py.
You can always do this from the terminal:
$ python3 script.py
Alternatively, you can make the script executable.
This requires that the first line of the script give the path to python3:
#! /usr/bin/python3
If you don't know where python3 is you can find it like this:
$ which python3
Now we need to tell the OS that script.py is an executable file type.
To make a python script script.py executable:
$ chmod +x script.py
Now you can run the script like this:
$ ./script.py