need two voices in one staff

Hi! I love MuseScore but I'm a bit puzzled as to how to enter two voices in once staff. I have a set of notes whose stems point upward and a set of notes whose stems point downward. When I try to enter a second voice into the measure (this is for a solo guitar piece), the software tries to tie the new note to the other voice and I don't want it to do that. Can you advise me if there is a way to accomplish this with MuseScore? -su