Compilation of the executables ought be as easy as

  make EndNote2bib dosToTex r2bib EndNoteTag
  make wileyEndNoteFilt ansel2uni risDateAdj

as supported by the Makefile template, see make(1). These programs
are independent. If compilation of one or more of these fails
--for example because lex(1) or flex(1) are not installed on your
system--, the others can still be compiled and run individually.

Alternatively the gcc compiler and/or lex compilers can be used,
in the minimalistic cases without optimization similar to:

  cc -o EndNote2bib EndNote2bib.c
  cc -o dosToTex dosToTex.c
  cc -o r2bib r2bib.c
  c++ -o EndNoteTag EndNoteTag.C

In particular, some tuning of the behavior of ansel2uni(1)  is only
supported by running lex(1) and cc(1) separately, using preprocessor
options for the later.

The man(1) pages ought be copied to man/man1 directories that are in the MANPATH:
   echo $MANPATH
   install *.1 -t ..../man/man1

Otherwise they can be looked at in the style of nroff(1) through a pager,
   nroff -man EndNote2bib.1 | less
   nroff -man EndNoteTag.1 | less
   nroff -man risDateAdj.1 | less
   nroff -man wileyEndNoteFilt.1 | less
   nroff -man ansel2uni.1 | less
   nroff -man dosToTex.1 | less
   nroff -man r2bib.1 | less