When you only use Pascal code, and Pascal units, then you will not see much of the part that the linker plays in creating your executable. The linker is only called when you compile a program. When compiling units, the linker isn’t invoked.
However, there are times that linking to C libraries, or to external object files created by other compilers, may be necessary. The Free Pascal compiler can generate calls to a C function, and can generate functions that can be called from C (exported functions).