This article takes you through the process for acquiring an Asset Package from Marketplace. if you haven't already made a made a YoYo Games Marketplace account you should do so now. This can be done from within GameMaker: Studio by clicking the "Marketplace" menu and selecting the "Login" option. The log in window will have a link that you can click to create a new account. you can also do this from a browser by going to the YoYo Games Marketplace.
NOTE: You will also need to have purchased GameMaker: Studio Pro (or higher).
Once you have created your account and logged into Marketplace, you can then browse the available asset packages available. You can download official YoYo Games content, or content created by other community members, and the content can be either paid or free.
Buying A Package
If you are buying an asset package for GameMaker: Studio you simply have to select it from the market listings and click the "Buy for..." button. This will add the product to your cart, and you can either proceed to the checkout or continue to browse the assets and add further purchases. When you are ready to proceed with the payment, you can select the "Cart" option from the top right of the screen and you'll be taken to an overview of the products in your cart.
If everything is correct you can then click the "Continue" button to be taken to the checkout. Here you pay through a credit card purchase.
When you have completed the payment, you will be shown a "Purchase Complete" screen where you can print out the receipt. You will also be sent an email with the payment confirmation details. Once you have completed a purchase (either of a free asset or a paid one), you can go to the GameMaker: Studio Marketplace window (which can be opened from the "Marketplace" drop down in the IDE), and click on the "My Library" tab.
GameMaker: Studio Library
All of the asset packages that you buy are listed in the "My Library" tab of the YoYo Games Marketplace window within GameMaker: Studio.
From here you can download the assets to your computer, and also add them to the current project - adding them to a project will download them first before adding them into the resource tree. Once they have been added, they will have their own folder to make locating them easier.
NOTE: Packages are downloaded to the local app data folder for Game Maker: Studio - %localappdata%\GameMaker-Studio\lib
With the assets added to your resource tree, you can now go ahead and use them in your game as you would those assets that you have created yourself. You should note, that assets downloaded form Marketplace are for individual use and cannot be shared to 3rd parties.