Your puppy was litter box trained starting at three weeks old. It is accustomed to going in a potty area and not in it play/sleep area. This makes training your puppy to potty outside easier. Your new puppy will need to potty very often. I suggest the following:
Taking him out as soon as he eats, when he wakes from a nap, when he is taken out of the crate, early AM, and late PM, and anytime it has been a while since he has been out.
When you are not watching your puppy leave it in the crate or small play area. It is important to "catch" your puppy if it has a potty accident so you can take it outside right away. If you see your puppy start to squat say “outside” and pick it up and take it outside and then say "go potty" (or whatever term you use). You should also reward when puppy “goes potty” outside. If you are using the bell, make sure to help your puppy to ring the bell when you take it out to potty each time.