Initiatory (adjective)

1. Serving as an introduction or introduction to something.
2. Relating to initiation or the state of being initiated.

Origin:

Late 16th century: from french initiatoire or latin initiatorium, from initiare 'begin, initiate', from initium 'beginning'. the current sense of the word dates from the late 19th century.

Examples:

1. The initiatory ceremony marked the beginning of the initiate's journey.
2. This book provides a thorough initiatory guide to the subject.
3. The initiatory period of learning is important to lay the foundation.
4. The initiatory class is necessary for all new members.
5. The initiatory phase was necessary to understand the concept.