In case you don't know, flies look like, well, flies. Or some version of flying insect. Or insect larvae. Or small fish. I saw one made to resemble a prairie dog. But to start with there are 3 different kinds. Dry, nymphs, and streamers
Dry flies are meant to resemble insects. The ones that land on the water and become food. May flies are really popular. If they breed where you are you know what I mean.
There are also crickets, grasshoppers, and any other insect in your area. You want your flies to resemble what is available in your neck of the woods.
They float on top of the water like a little stranded and helpless bug. Fish go for the easy prey faster than the ones they have to work for. Usually. (That word gets used a lot in fishing.)
Nymphs are the insect larvae. They sit just below or at right at the top of the water. 90% of what fish eat is under the water. So, this is a very productive fly to learn. It's also a little bit tricker than dry, but worth the effort.
Lastly, but not leastly, we have streamers. They resemble small fish or other, larger, aquatic life. Leaches would fall into this category. They use different retrieval methods to try and mimic the aquatic life form they resemble. Once you get the other basics down move into these.
So, there they are. The flies of fishing. Learn them in the order presented. It's usually easiest that way. Dry, nymph, streamer. Some people skip nymph and learn them last. But it's up to you. Eventually you'll know them all. Be patient. This is a lifelong endeavor not a weekend getaway. But it is nice to get away for the weekend and just fish. You'll see. I guarantee.