The number of days decides most of it. With 2 or 3 days, every session trains the whole body, so each muscle still gets worked two or three times a week. With 4 days, an upper/lower split trains everything twice with shorter sessions. 5 days add a push, pull and legs block to an upper and a lower day. 6 days run push/pull/legs twice.
Your goal sets the reps and rest: heavier and longer rests for strength, 6 to 15 reps for muscle, denser sessions for fat loss. Beginners get fewer sets per exercise; advanced lifters an extra set on the big lifts. Session length decides how many exercises fit, counting the time under the bar and the rests.