I want to be a back-end developer. And i know java. So how to implement this language to back-end or what's next, how can i use this? [closed]

please direct me a way from this. I have studied java in college. And iam pretty much good at it. And when get the aim of a back-end developer, everyone are saying to start with java, So i know java already but don't know how to use it in the back-end or i don't have the way to the next phase. Can you guys please help me with it