eyy boss nice to see that you are interested, I don't know much but I can point you to resources and give some general tips, learn languages(Java(is relevant to android stuff), C). I think you can use metasploit to create a backdoor which the victim has to run for his phone to get "hacked" but if you want to actually learn how all this works, you need to learn about how android works, a bit of ARM assembly may be required to write exploits, basics of networking.
This website might help you to learn all that
Click here(0x00sec.org), it will be more useful if you post the query there, more experienced people can guide you, this forum is waayy to broad for what you are looking.
@hawkk was into all this till he got banned for some reason,
@rone also seems to know his stuff so you can ask him if he is okay with it ig.