Customer Portal on Zoho Desk

Customer Portal on Zoho Desk

Hi, I'd like to know more about the items below I found when setting up the Customer Portal on Zoho Desk.
Could someone help me explaining these in details? Especially the 2nd and 3rd point.

Thanking you in advance!

Permissions
Customers can sign up for Customer Portal
Customers can view tickets of their organization (contacts)
Customers must register to access Customer Portal
Display Community in Customer Self Service portal