To breed hybrids, you need two of the same species of flower next to each other, either right next to each other or diagonally, with enough space for more flowers to spawn around them. Watering them increases the chances of new flowers spawning the next day, and it increases more if you water them on consecutive days, and especially if another player visiting your town waters your flowers.
This guide shows how to get all of the colors of hybrids from breeding. Gold roses aren't on it because you can't breed them, you have to water black roses with a gold watering can like KAYYBE said. But you'll also need to know how to breed black roses, so here you go: