Knowing your banjo is out is half the job. The other half is knowing which string, and which way to turn the peg.
Out of Tune plays the four GDAE strings with one of them off. Tap the string you think is wrong, then say whether it was sharp (too high) or flat (too low). Compare again plays it next to how it should sound, so you can hear the difference.
That's exactly what you do when tuning by ear, at home or before a session: find the string, decide up or down, turn. Easy puts the string a quarter-tone out; Hard narrows it to about a fifth of a semitone.
GDAE is the fiddle and mandolin tuning too, so the same ear carries straight over.