ThinLisp programs are Lisp programs. When developing programs you have access to a full Common Lisp programming environment. At runtime you are limited to a extremely efficent subset of Common Lisp, for example by default there is no garbage collector.
To writing a ThinLisp program you will need a Common Lisp programming environment; for example: CMU Lisp, Franz, or Allegro. You will need to be comfortable writing in simple Common Lisp and C.
The usual ThinLisp program is writting and tested in a standard Common Lisp environment. Once working it is then translated into C code using the ThinLisp translator. This C program is reasonably straight forward C code. The resulting C code maybe shipped directly or compiled and linked into an executable and shipped.
The package "THINLISP" or "TL" plays a role analagous to the package "COMMON-LISP" in standard Common Lisp holding the set of symbols who's behaviors define the ThinLisp dialect.
By convention ThinLisp programs are compiled in one of two modes, development and production as indicated by the symbol :development on the *features*. Authors typcially include additional checking and debugging facilities in the development version.
... So much more to write ...