This happens because you need to add the path to python executable to the environment variables. Use the following steps:

1. Open anaconda prompt
2. Inside anaconda prompt write the following command: where python It will display the python executable path it should be something like: C:\Users\<your_user_name>\AppData\Local\Continuum\anaconda3\python.exe
3. Copy the path without the \python.exe part
4. Open windows search and write environment variables. It should display something like Edit Environment Variables For This Account or Edit System Environment Variables. You can use any of them, click and open. I modify the one on my account since I don't have Admin privileges. I will use my settings in this example.
5. In the User's Variables double click on the Path variable. I'll open a new window.
6. Click new, and paste the path you copied before.
7. Now, there is another path you should add. Its the same as the one you just added but with the Scripts folder appended, like so: C:\Users\<your_user_name>\AppData\Local\Continuum\anaconda3\Scripts
8. Click on OK button in both windows to save your changes.
9. Next. Open cmd and write conda init cmd.exe
10. Open or restart cmd and write conda activate base
11. Then try it by typing python. It should work

Every time you open cmd to use python, you should activate it by executing the conda activate base command before using it, so you don't run into any trouble when it comes to load libraries.