introductory

1. Of, relating to, or constituting an introduction.
2. Serving to introduce. See synonyms at preliminary.

adjective

1. Of, relating to, or occurring at the start of something: beginning, inceptive, incipient, initial, initiatory, leadoff. See start/end.
2. Before or in preparation for the main matter, action, or business: inductive, prefatory, preliminary, preparatory, prolegomenous. See start/end.
3. Serving to introduce a subject or person, for example: prefatory, preliminary, preparatory, prolegomenous. See start/end, words.

Definition: preliminary, first
Antonyms: concluding, ending, final, finishing, last

The adjective has 3 meanings:

Meaning #1: serving to open or begin

Meaning #2: serving as a base or starting point
  Synonym: basic

Meaning #3: serving as an introduction or preface
  Synonyms: prefatorial, prefatory