What do you mean by "last threads"? Do you mean the new threads? Or do you mean the latest threads with new posts in?
If you mean new threads, just create a new widget in the ACP and choose the Widget definition "new threads".
If you mean latest threads with new posts, then that's the New posts widget which you should already have that effectively does this (see the main page of this site for an example). If you don't (e.g. if you have deleted it) you can recreate it by creating a new widget and choosing the widget definition "new posts".