Hey Philip,
These tutorials in the learning paths can be pretty tricky. There is a chance some of the weirdness can be because you are using a different version of studio pro than the tutorial (I must have 15 different versions on my machine by now lol).
But you should be able to add a button to a container inside a gallery element, below is an example in how it might look in the Page Explorer (on your left sidebar)
In general I use the design made pane when I'm seeing how things look, but for adding things I find dragging it into the page explorer or moving to "Structure Mode" (in your top-bar of studio pro) is easier to place things.
There's a chance that something else is going on, feel free to put some screenshots in here with some more info if that doesn't help!