A common selection is to find a particular contributor, someone whose work you've grown to admire.
To add a contributor to your selection, click the "Add" button. A pop-up will ask you for the first few letters of the contributor's last name and then display a list of contributors sorted from there onward. If you don't know the contributor's name, use the search form for the contributor, and then come back here after you know.
Note that there is no and/or selection possible between the contributors. They are all "or" selections, that is, we will find mblogs from either of the contributors you specify. That's because a search for mblogs by both contributors would always fail to yield any matches since all mblogs are designated from one contributor.