Action Details
Requirements and how-to articles for Facebook's action:

Groups allow people with similar interests to share posts and communicate with each other.

You need this to get it done:

Group Name
Choose a name for your group. Try and keep it short but with enough information for people to be able to tell what your group is about.
Add Group Members
Add some people to your group using their names/email addresses (at least one person other than yourself.)
Cover Photo
Recommended size: 1,640 x 856 pixels (1.91:1 ratio)
Write a description with information about your group.
Group Type
Choose the type which best describes your group ("General", "Buy and sell", "Gaming" or "Social learning".) This allows you to have access to features which fit your group's needs.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Facebook Help Centre - About Groups
Information about Facebook Groups.
Link missing here or found errors? Improve How-Tos