Sometimes, it's easier to learn when you see new things a little bit at a time rather than all at once. When reading an explanation, it might show you more after you answer a question correctly or say you're ready to continue.
Every time an explanation pauses for you to be ready, you'll have an option to expand the explanation. If you want to just go ahead and see the whole explanation at once, click the "Expand" button. Be careful of spoilers!