Important: Students should be directed towards the student guidelines for online forum etiquette, it is a good idea to include a link to this in any forum introduction.
Unless you expect students to want to get RSS feeds of the forums you should leave these settings as the default. If you do intend to use the RSS feed you should set the settings to control the format of the feed.
Using the Grade settings you can choose to grade posts as assignments and have those grades entered in the gradebook. However you will probably find it less time consuming to calculate grades based on an activity report and enter a participation grade into the gradebook by creating an offline activity.
Post threshold for blocking
You can use these settings to restrict your students from posting after a given number of posts.
Common module settings
The most important of the common module settings is the Group settings. This is covered elsewhere.
For more information and useful tips on setting up forums and fostering participation and a sense of community visit the moodle.org documentation site: http://docs.moodle.org/en/Forum_module#The_News_Forum