Your public profile shows the opinions that others have about you. This way, everyone will know how do you work and what others have felt when working with you. Good references can help you a lot!
You can write your opinion about any other user by entering the section "options" you'll find in every public profile.
When someone writes an opinion to you, you'll receive a notification email, and you'll have to validate if you want it to appear in your profile.
Write your opinion about all the people you've worked with, this will help them a lot, and sure they will also help you by writing their opinions about you!