Here At Horace Green (from School of Rock: The Musical) -

1. Searching

In the search bar (as depicted alongside), type the title or artist/composer you're looking for. The search results appear as shown below. When you click on the desired title, you will see the item page with a preview of the first page of the piece of music at the bottom. There's often also the ability to listen to the music of the first page using the play button.

2. Purchase of the product

You can add the item to the cart and checkout. This can only be done with iDeal and an account, as the item can only be printed from your account. An account is easy to create.

3. Log in to your account

After checkout, you can find the ordered song in your account under the heading "my digital sheet music".

4. Printing

Behind the title(s) is "view" and clicking on it will provide a preview page with a print icon at the bottom.

After clicking on the print icon, you will get a warning screen: make sure there's enough paper and ink in the printer, the margins are set correctly, etc. You can really only print it once.