for android mobile dev
do we really need to learn retrofit?i know that is part of RestApi, but retrofit is really hard to learn and less tutorial about it,maybe if anyone good information its really helpfull for begginer like me,thanks.

You could juste use normal http requests and parse the json. Maybe write some helpers for your specific api.

If you want to get a job, yes. For basic usage, it's pretty simple to use.

You can consider using smth like ktor tough.

Yes, in almost every project that I've worked had the retrofit implemented, we have others ways as using the HttpClient "directly" as the retrofit do. There are libs as ktor that also gives you a way to communicate with a REST API, but retrofit for sure is the major one.
What I did when i was learning was learn how to make the communication in a low level and then I when U tried to learn the retrofit it was easier.
If u have any doubt about it you also can call one of us, even in PT-br, my language, we have a lot of good article about it, and in English Im sure that you can find a good piece of work, examples on GitHub and Medium.
Anyway, I can try to help you with it if you wanna

@rittmann thanks bro its really helpfull,for now i still learn GET and try to focus on it

@WildOrangutan is there many kotlin job out there?

@Siko Kotlin is basically requirement for Android development. Not sure about other platforms, but it's getting very popular, especially in favour of Java.

Use okhttp instead then.

@Siko yes.