Good advice. I always start beginners out at 66 bpm, two notes per beat. That means if the song is mostly quarter notes, each beat is the equivalent of a half note. If the song is mostly eighth notes, each beat is the equivalent of a quarter note. If 66 is too fast, drop it down to 56. If it's too slow, speed it up to 76. You'll get a feel for what's appropriate pretty quickly. For really difficult stuff, keep the speed the same but make each beat one note.
Don't worry too much about speed. For a beginner, the metronome is all about developing timing. When my son was learning, for months we didn't play anything faster than 86. Now he can play stuff at 160 and above, but his timing is good because of all the time he spent playing at 66, 76, 86, and sometimes 56.