Pick values and save to XREF table

I work for a non-profit organization needing a program to record information
on staff members who accept speaking engagements. I have background with data
and analysis, but I am not a programmer. I've played around with Access for
several years using ODBC to SQL DB, macros and wizards, but know nothing
about how to code. I hope someone in this forum can help me.

DATABASE (partial, but same structure used throughout)
Table: Message; Columns: MessageID AutoNum PrimaryKey (PK), MessageTitle Text
255 Not null
Table: Topic; Columns: TopicID AutoNum PK, TopicDescr Text 50 Not null
Table: MessageTopicXREF; Columns: MessageID PK, TopicID PK
Relationships: Message --- MessageTopicXREF --- Topic; Message can have 0
to many associated Topics (basically a list of ~150 reusable "Key Word"
values).

FORM
I have one mainform with tab control and Menu that I borrowed from one of the
MSAccess templates. The form header displays the Message Title with a Search
button. Each of the 4 tabs has 1 or more subforms to display existing data.
Edit functions are disabled since most users will view only.

MY PROBLEM
I have storyboarded a button "Add Topic for this Message" with the idea that
button would open a new window listing available topics (filter out topics
already linked to message, no new topic entry allowed). Select Topic from
list on new window, then use ADD button to write record to MessageTopicXREF
table (MessageID from Main form and TopicID). Refresh select list and allow
additional Topic selections. Mutiple selection of topics is not a requirement.
Close would write record, if anything is selected, then return to Message
mainform on the same tab with refreshed data. I need to use this same pattern
for 6 different XREF tables.

I would sure be grateful for any help but please remember that I'm not a
programmer if you respond.