GameMaker has a folder setting for where the project templates are stored. You can find it in File -> Preferences -> Paths

Set this folder to your desired destination, you don't have to stick with the GameMaker default,
and then extract the gml-raptor-template-x.y.zip project template from this repository to the folder set here.

Many people struggle with unzipping and the resulting folder structure. Make sure, your project templates folder looks like this and in the folder, the template files are directly visible, without any additional subfolders, as shown in the picture below:

You will find two command scripts (one for Windows, one for Linux) after extracting the zip.
To have the template show up in your GameMaker Studio, run the script for your OS. It does nothing complicated, just adds a line into the template_projects file of the GameMaker settings.

Having the template in place, you simply click on New at the start screen of GameMaker,
switch the template view to User Templates, and the raptor logo of the template should appear.

Click it, set a name and folder for your project, and you're ready to go!

Continue in Project Template Overview.