Understanding SQL Queries (Subqueries, where Clauses

There are three tables in the DB on SQL: user, audit, and changelog.
The columns are as follows:

[user]
id,email,date

[audit]
user_id, difference_id, date

[changelog]
difference_id, log, year, month, date

※ user.id and audit.user_id are common data

I would like to index user.email from changelog.difference_id, but I would definitely like the where clause to include where date_format (CURRENT_TIMESTAMP, '%Y%m%d') and return the result by date.
I'd like to consolidate the queries into one, but I don't know how to describe the subqueries. (Specifically, I'm confused by the situation where there are multiple conditions and I'm using subqueries.)

In short, I would like to summarize the following two queries and submit the one with the date today (dynamic).
select user_id
from audit
where changelog.difference_id='{{9fjei347fyw83926r}}'
Return →user_id=1007

select email
from user inner join audit on id=user_id
where user_id='{{1007}}'

I'm a beginner, and I don't know what it means, but I'd appreciate it if you could teach me as gently as possible.
I look forward to your kind cooperation.

sql

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