Both Uses of

initiate
in
The Adventures of Tom Sawyer

We'll get the boys together and have the initiation to-night, maybe.†
Chpt 35 *

initiation = the process of accepting someone's membership though a special procedure such as a ceremony and/or period of instruction and/or test

Definitions:

(1) (initiate as in: initiate discussions)
to cause (something) to begin
(2) (initiate as in: initiate into the art of drumming)
introduce to an activity or area of knowledge
(3) (initiate as in: initiate into the fraternity)
to accept someone's membership into an organization -- typically in a ceremony -- sometimes including a period of instruction and/or test
(4) (initiate as in: She is a new initiate.)
someone who has formally started in an organization, or been introduced to or attained some expertise in a particular field