Building muscle is at once very simple and simultaneously incredibly complicated. If that sounds like something of a frustrating contradiction well then get used to it, as you learn more about growing muscle and getting jacked you’ll find that almost all the information you come across only makes things more complicated and more difficult. Everyone has a different opinion and no-one seems able to agree on what the best way to get into powerful shape actually is.
When you start out though, it all seems very straightforward. In order to grow, you need to exercise more and eat more protein. When you do this, you start to build more muscle and you see yourself constantly increase in strength. If you aren’t seeing any growth or strength gains, then it might well simply mean that you aren’t going to the gym regularly enough, or working out hard enough when you are there.