What is the Contributor role? How do I become a contributor?

Becoming a Contributor allows you to earn more Pi by building a security circle of 3-5 trusted members. 

Pi’s Contributor role becomes unlocked for users after you’ve finished 3 mining sessions as a Pioneer. After 3 days of mining, you will see a new icon of the security circle on the home screen of the app which you can click to start. To become a contributor, you need to add 3-5 people who you trust to your security circle.