If you see a yellow star next to a skill, your teacher or parent is suggesting that you practice it. You can still work on any skill you want, but keep an eye out for those yellow stars!
If you are a student, you can also go to your Recommendations wall to see all the skills suggested to you in one place. Click on skills suggested by your teacher in the upper-right corner to view them!
If you are a teacher or parent and want to learn more about highlighting specific skills, please read Is there a way to suggest skills to students?