Anaconda

Download Anaconda Python from https://www.anaconda.com/distribution/. The remarks below refer to the command-line version of the installer.
Run the installer, but first read through all of the remarks.

If on Windows, you might need to run the downloaded installation file as administrator, depending on the choice of the installation directory (right-click the file, and click "Run as administrator").
Do not use the default installation path if it contains spaces or other special characters. We do not know exactly when this could turn out to be an issue, but it is discouraged by Anaconda (more info here). For instance, if John Doe ran the installer, the default path might be C:\Users\John Doe\Anaconda3, which could be an issue since his username has a space in it. An alternative would be C:\anaconda3, although this would probably require you to run the installation as an administrator.
During the installation, make sure to select the option to add Anaconda to your PATH environment variable. As far as we know, this is usually not recommended by Anaconda and thus deselected by default.
You do not need to "Register Anaconda as the default/system Python"

After installation, run the command conda init (or optionally conda init <SHELL_OF_YOUR_CHOICE>), in order to set up conda to work properly with your command-line interpreter (terminal). You may have been asked for the conda init step to be automatically carried out during installation, but if not it is essential that you do it manually, in order to be able to activate your Conda environment later.
Close all terminal windows currently open (the conda init step above will not have any effect on existing terminal windows, only on new ones).
If you are new to Anaconda, we recommend you have a look at this short tutorial.