Install python from this link 
https://www.python.org/downloads/ 
After this, install it on your PC. Look for the location where PYTHON has been installed on your PC using tge following command on your command prompt: cmd python. 
Then go to advanced system settings and add new variable and name it as PYTHON_NAME and paste the copied path. 
Then look for the path variable, select it's value and select edit 
Add a semicolon towards the end of the value if it's not present and then type %PYTHON_HOME%