Joining a Facebook group gives you access to a news feed about a common interest or cause. A group's home page includes a "Wall" of news. If the group administrators allow FB members to post to the group, you can type your post in the screen's text box. Your fellow FB members can view your shared announcements or feedback on the group's Wall.
Open the Facebook group home page.
Click the "Wall" tab, and a list of announcements appears.
Type the post in the "Share" section just below the "Wall" tab. This text box is labelled, "What's on your mind?" or "Write something ..."
Click the blue "Share" button. This button is located just below the end of the text box. Your new post appears on the Group's home page.
The group Admins can customise the page to allow non-admins to post to the Wall.