You can add a GEX legacy extension straight into your project
resource tree y right clicking on the extension resource and
selecting Import Extension (you will need to change the file
selector to point to GEX files), which will open the following
In this form you can indicate which GEX extension packages must be
used in the game you are making. On the left there is the list of
Used packages and on the right is the list of
Available packages, and to move a package from one list to
the other, simply select it and press the button between the lists.
When selecting a package a short description is usually given at
the bottom (but not always if the package has been made by third
party developers), and further help may also be available by
pressing the Help button.
To install new GEX packages or uninstall existing GEX packages, press the Install button and the following window will open: You can see a list of all extension packages available (these are stored by default in the "Extensions" folder of the root directory where you have GameMaker: Studio installed). By selecting a package and clicking the Uninstall button the package is removed from the system, and pressing install will open a standard load file window where you can select a new package from your computer to make available within GameMaker: Studio.