OK, first off, remember, this is just a game. No one will take your money away or beat you if you fail.
Second, you don’t need to be afraid of them. Sometimes you don’t win in this game, and that’s all right. When I was first building a Machamp team by doing Machamp raids, I struggled with Dynamic Punch, but I could beat Close Combat. Then I got a handle on Heavy Slam too, and finally I got good enough to beat DP. With a little more work I could even beat them weather buffed. That’s the model.
For all the rocket leaders, they have different teams. Some are easier to beat than others. Read over the guides, and try your best strategies against one or another. If you fail a few times, accept that you’re not ready for that combination, heal up, and move on to another. The good thing about the rocket leaders is that if you fail, you keep the rocket radar, and can try again. In my efforts to get better at beating Machamp, once I spent the raid pass, it was spent, and I got nothing if I couldn’t win.
Another good tip: since the first pokemon is always the same, get yourself in a position to beat that one soundly and have some farmed energy to hit the second pokemon with. Even if you don’t beat the combination, you’ll get better at fighting their lead pokemon, which is useful and good.
Finally, remember that the strength of the rocket leader’s pokemon is a function of your level. I occasionally help my friend by playing his account for him (he’s level 32, I’m 40). The foes he sees are significantly less powerful than the ones I see in the same battle. So just waiting and leveling up isn’t going to make it easier; it might get harder. What you need to do is focus on getting you better at having the right pokemon for the fight you’re in, and using them better in that fight. That’s the secret to beating the Rocket leaders. It isn’t that hard. If you can’t get there yourself, find a local mentor who can help you get over the hump.