The puppies will require some time under supervision before they're more comfortable with each other. You have to make sure that they don't fight under any conditions. One fight could completely ruin their whole future together. It's incredibly important to prevent aggression. Make sure that they're kept in different places, and when they're together, you're there to make sure nothing bad happens.
The best way to set up a meet between a newer puppy to an older dog or any two pets, in general, is to avoid any sort of territorial behavior. Puppies tend to be very protective of their spaces and their toys as well. Make sure you put away your older dog's toys. Moreover, introduce them in a place that is neutral to both puppies. Your driveway, the backyard, a public park, all of these are great ideas.
Dogs tend to show aggression to one another when it comes to food. Dogs that lived together since they were a baby sort of getting accustomed to eating out their own bowl. But, if you introduce grown-up dogs to one another, they're going to finish their own plate as quickly as they can and try to lash out on the other dog's plate. You have to prevent this behavior; otherwise, it could spark aggression between your dogs.
One of the worst things that a puppy feels in the presence of another animal is its invasion of privacy. They're very protective of their places, especially the place they sleep. You have to make sure that even though they might get along well, there should be places where the two puppies can get away from each other.
The first time your puppies meet, they will want to discover each other. They'll sniff the other dog, maybe even lick them. This is basic dog behavior as they start to get to know each other. Don't restrict them. If the dogs are growling at each other, that's aggressive behavior. But, if there isn't any aggression, let them get in contact and meet each other without any restriction.
Socialize your puppy