Welcome to the bobble stitch! This is used quite often in the beginner Christmas crochet patterns you will find on the blog, so I thought I would link to it separately rather than repeat the steps a bunch of times. The stitch is a really quick and easy way to make a pom pom shape without having the faff of cutting yarn. You can use them as the top of a Christmas Tree or the bobble on a Santa Hat. I love to work these using a glitter yarn to get a bit of extra sparkle, but you can use whatever yarn goes with your project, the stitches will be the same but the overall piece may end up smaller/larger depending on the yarn weight.
Chain 2, yarn over and pull up a loop through the first chain as though you’re going to work a double crochet. With 3 loops on the hook, yarn over and pull through the first 2 loops, then stop.
Yarn over and pull up another loop through the same stitch. Yarn over and pull through the first two loops, then stop with 3 loops on the hook.
Repeat these steps within the same stitch until you have a total of 6 loops on the hook, then yarn over and pull through all 6 loops together.
Close off and cut a tail to use to join to the rest of your work.