Now that you know what you have available to work with in creating your Ghost theme, you can begin making decisions on how to put the available elements together. You'll find what is essentially a quiz that you can run yourself at the beginning of each new design in this section.
These questions are not intended to give you hard-and-fast rules you must follow, so if you want to do something not covered here, by all means, feel free. But as you kick off your learning process, they will give you a simple method to make commencing a new design much easier.
If you have an idea in your mind already, you can go through and answer the questions in a way that fits what you're imagining. And if you don't have any ideas yet, you can just decide on your answers as you go along then when you'll have the basis of your design in place, ready for the next section.