I downloaded and installed the loops but they don't appear anywhere.
Where are you looking for the loops? It is not easy to tell, if the in-app purchase has been installed.
The in-app purchase will not be visible as an extra purchase. There will simply be more of everything. For example, when you add a drum track, there will be more drummers to pick from, like this: Do you have more than one drummer?
If you do not see your new Loops in the Loops Browser, reindex them: There should be 2000 loops.
Click the heading "Loops" aat the top pf the loops browser and select "Reindex Loops" at the bottom of the drop-down menu. That should take some time, but find all loops you have installed. On a small screen the loops may not show in the Toolbar. If the Loops Browser is not shown in the Toolbar, click the double ">>" to disclose the Loops menu.
And you should see more Lessons at the Lesson Store.
One more thing. There is a funny quirk at the appStore. To be able to make in-app purchases, you first need to make a regular purchase, buy a song from iTunes or somesthing. That will set up your account correctly.