How do I create those beautiful hybrid flowers? I always try placing them in different patterns, and I have no luck. Am I supposed to use fertilizer for them or what? Someone please help me.
Fertilizer can help. It can also help if you limit the flowers that you have out to the ones you want to breed, as the chances of producing offspring are much higher. You can fill a mule (additional character) with all the flowers you want to keep but not have out. But other than that it's just time.
I suggest you look up guides online. It's mostly placement of certain colors. Try placing two flowers that will breed a hybrid (check the guides online) and water them. A hybrid should appear. Although it might be rare, it should appear, at least 2-4. Less if it's raining.
There are a lot of guides online that you can look at which will tell you which flower colors to mix in order to get a particular hybrid. But some general tips that I've found helpful: 1) Plant the flowers you want to hybridize on the beach. Villagers won't plant random flowers there, and you'll never have a villager place their house over your nice hybrids. 2) Only water the flower types you want to hybridize. So if you're trying to get pink roses, only water your red & white rose pairs, and don't water any other types of flower--that'll increase your chance of getting that specific hybrid. If you really want to increase the chances of a specific hybrid you can uproot all the flowers in your town apart from the ones you want to hybridize.
Also, I've read that there are specific areas of your town that have a higher chance of spawning hybrids. I'm not 100% sure if that's true, but I have noticed hybrids in my town doing much better in certain areas than others. It takes a lot of trial and error to figure out these specific spots, though.