The applicant look-up screen is invoked from several places and is used to select one or more applicants.
If multiple applicants can be selected you can do so by using the standard windows methodology. Shift key plus mouse click to select a range or control key plus mouse click to add to the selection.
When all applicants have been selected click on the button in the quick access toolbar.
If you only wish to select a single applicant this can be accomplished by double clicking the appropriate applicant.