Blogger or blogspot is one of the best blogging service among all as you know. But there have some limitation as it is not self web hosted service for blog. You can post unlimited amount of articles there. but you can not create forum normally as other self web hosted blog can do. Forum is a discussion board which is very Effective. And if you add a forum service with your blog then it will be very helpful.
So i am going to tell you how to make this. It will not looked like Mainstream Forum But it is useful. People can easily ask any question and give any answer. You can create this by adding embed code of forum service provider. Please follow the steps if you want to do this.
1. Open http://www.nabble.com/
2. Click Start a Free Forum.
3. Fill up the Form.
4. Your Forum will be created.
5. Now to get Embed codes you have to Register and log in to Nabble.
6. After log in Click Options -> Embedding options.
(Next you have to put the codes into your blogger)
8. Log in to your blogger account and open your dashboard.
9. Click Pages and add new page.
11. Publish your page.
You are Done! Now you can see your Forum page.