To compile the lisp start up program, you should be in the top level directory of the sources (/usr/lisp) and type:
make lisp
This will compile the file lisp.c, assemble the file lispstart.s and produce an executable file lisp. Currently the default location for the lisp core file is /usr/misc/.lisp/lib/lisp.core. If you want to change this default location, edit the file lisp.c and change the line
#define COREFILE "/usr/misc/.lisp/lib/lisp.core"
to refer to the file where you intend to put the core file.
This step takes a few seconds.