In B/X, monsters have more various attacks. For example, an Owlbear has: 2 claw/1 Bite that deals 1d8 damage each. But how does this work? Can they use one attack per turn or all their attacks in one turn? Do they have to roll "to hit" for every attack or just one for all their attacks? Do they have to attack just one target or more?
They get all their attacks every round, and roll to hit separately for them. They can even move and use all their attacks—it's not like D&D 3e, with its "full attack" limitation!
They can split up their multiple attacks against as many engaged opponents as they like. The exception to that is if the description specifically says that they have to attack the same target, but that's pretty rare.
Sometimes you'll see a line like "claw/claw/bite or weapon", in which case they get one set or the other, not all of them: e.g., two claw attacks and one bite, or one weapon attack; not 2 claws, a bite, and a weapon attack.
Yes, creatures with multiple attacks are nasty and dangerous! Make sure you warn players who are B/X novices that such creatures are not to be underestimated.