When you put a full stop in, you'll usually need to change the wording immediately afterwards, so that the new sentence starts logically. Typically, it's best to have just one or two ideas in most of your sentences. There is now some more advice on how to tackle this particular example. This is the hint that appears in the course.
Obviously, you haven't worked through the lesson on keeping sentences short, and why this is so important. So here's a bit of help: look for the individual ideas that are in each sentence. You'll see that there are five or more in each one. Look for where one idea ends and another begins. These are points where you may be able to put in a full stop.