If you have successfully completed all of the lessons so far, you can crochet. But think how boring crochet would be if you couldn't shape the simple rectangle we made in the first lessons into something else. There wouldn't be any incentive to learn the craft! That's why the rest of the lessons in crochet school are about turning the stitches we have learned into pieces. And the easiest shaping technique you can learn is how to increase.
Again, like most of the things we'll learn before we learn how to read patterns, increasing is usually written into patterns. It will say something like "make 2 dcs in next st (stitch), dc in next 3 sts, then make 2 dcs in next st." However, if you come across a vintage pattern, it may say something like "crochet 5 inches of dc sts increasing 15 sts evenly over the rows." That's where some math will have to come in and you'll have to figure out how many rows of double crochet stitches will equal 5 inches and then how many increases you'll have to make per row to equal 15 more stitches. We'll talk about this more as we get into reading patterns.