Building software from source requires to work in a console window and some familiarity with build tools like compilers, GNU Make/CMake, makefiles, text editors, etc.
That is something you best obtain from somebody in-person (i.e. that does have the experience and look over your shoulder or that you can share your screen with). It is definitely beyond the scope of this mailing list. The specific details of the build procedure for LAMMPS (either using GNU Make or CMake) is explained in great detail in the LAMMPS manual.
It assumes the aforementioned familiarity, but you don’t have to be an “expert”. Specifically the build procedure with CMake is designed to make most choices automatically and supports either a GUI or a menu driven text mode interface. A small tutorial for using CMake to build LAMMPS is included in the HowTo section of the manual.