Click your icon in top right menu and choose profile.
Once in your profile you will see various settings. click on edit.
You will now see options to edit the various details in your profile.
NAME: Add your real name or nick name and optional surname.
HOME LIFE: Add where you live and relationship status etc.
WORK & EDUCATION: Add your work place, skills you want to share & schools or unis attended.
ABOUT ME: Add birth date, about me, hobbies and website link etc.
Apart from main display name, all options are optional.