First, let's cover the basics: to make Jello, you'll need to dissolve the Jello powder in boiling water, then add cold water to help it set. But what about the fruit? Do you add it to the mixture before it sets, or after?
The answer depends on the type of fruit you're using and the texture you're going for. If you're using soft fruits like strawberries or bananas, you can add them to the Jello mixture before it sets. This will help distribute the fruit evenly throughout the Jello.
However, if you're using harder fruits like pineapples or apples, it's best to add them after the Jello has set. This will help prevent the fruit from breaking down and making the Jello too mushy.
Jello Layer Cake Recipe at Arthur Dwyer blog