Do I have to press xzxzxzxzxzxzxzx like this very fast or do I have to change finger whenever the slides and circles change color?? I can only play with one finger and I'd like to learn how to play with two so I can play harder maps.. Thank you!
You need to practice whit two fingers and get used to use them. Some people full alternate, that means that they end the song presing the same amount of times Z and X (or the keys you use). And others (like me) single tap whit one finger and use two fingers for streams and triplets.
It helps to start off easy so your fingers understand what you are trying to do. Once you're confident that you can alternate alright, then move on to what's the hardest map you can pass. If you pass the map, then your alternating skills should be pretty close to your single tap. If you get a better score, then your alternating is most likely slightly better than your single tap(in some ways).