The users in user role should be able to create new topics and should be the admins for their own topics. That is, they should be able to add/ modify /  delete their own topic

Users can add topics for discussions belonging to the group a user is member of, meaning the discussion needs to belong to the user's group. 

The user can only edit/delete his own posts, but he cannot edit/delete the whole topic, that's only reserved for administrators and moderators. 

If you want to achieve the effect you're looking for, you will need to code some custom logic for it.

Regards

I want the users to be allocated automatically to a group when they sign up. For example how this forum on yous site mono-software work. When I signed up, i got added to a support group and now I can add support posts to the forum. But I cannot see which group I am in. i just want the forum to be open for the users to add posts without creating a extra step of joining a group.

Thanks

Hello,

I believe you are confusing two "different" things. We have discussion boards which are stand alone forums and group discussion boards which are "tied" to a certain group. Your site can be configured to have multiple discussion boards while a particular group can also have multiple discussion boards. This support forum is only a standalone discussion board, it is not tied to any particular group. Let me know if this cleared up the confusion.

Regards,
Mario

How can you allow topics to be added by users in the Discussion board?

The users in user role should be able to create new topics and should be the admins for their own topics. That is, they should be able to add/ modify /  delete their own topic

This was my initial question. I want only discussion boards on my site where any user can add a topic.

The user groups available for checking when the discussion board is created determine the board access if board membership is enabled, i.e. which user groups will be able to see the board.

When it comes to editing/deleting content on the board, that is reserved for administrators and moderators of the board (notice this is on discussion board level, not per-topic level). 
Users are only allowed to edit/delete their own posts, but not the whole topic (again, this is for moderators and admins only).

What you asked for is that each user becomes a moderator/admin for his own topic and that functionality is not present out of the box and requires additional coding to be achieved.

You can do it yourself and ask for some additional pointers on how to do it, or you can issue a new feature request for future versions of MonoX in the roadmap discussion board.