Well, I'm going to try to answer with some assumptions.
I assume that you are new like me and had no concept of pip install.
Generally, if you are new, you think of downloading and pressing an exe. file to install something. You probably(I did) tried something like this and installed it incorrectly. Pip install tends to be very consistent and avoid making this an issue.
I find this to be a general benign issue with the coding community if you're brand new. There's just so many concepts that are taken for granted that explanation to beginners tends to be not so great. You have to be very specific and give a lot of context and your own thought processes to even type the right question.
Here are the steps:
1.Find where your python folder is located and write down the path:
C:\Users\yourusername\AppData\Local\Programs\Python\Python36-32\Scripts
2.Click on your windows start button and type "cmd" in the search bar and click on it to open that wonderful black box.
3.Now copy paste the address and add '\pip install selenium and hit enter
C:\Users\yourusername\AppData\Local\Programs\Python\Python36-32\Scripts\pip install selenium
All you need to now is wait for it to tell you to that it was successful. There are other functions for pip like uninstalling, updating and etc. Just so you know. Sometimes one of the annoying things for me is making sure I have the right term/name when I use pip install. Keep in mind that not everything is installed through pip, just most of the things you will use probably.
More examples:
C:\Users\yourusername\AppData\Local\Programs\Python\Python36-32\Scripts\pip install numpy
C:\Users\yourusername\AppData\Local\Programs\Python\Python36-32\Scripts\pip install openpyxl
C:\Users\yourusername\AppData\Local\Programs\Python\Python36-32\Scripts\pip install <libraryname>
This is the video that taught me how to install things:
https://www.youtube.com/watch?v=jnpC_Ib_lbc