Multiple Table Search

I want to do is search through a database based on what was selected on a form.It will be based on state, county, and category.Out of the search I just want one field out of the database, the email field. Now, at first I had one table to mess with so I was using this:

strSQL = "SELECT DISTINCT EMail FROM Info WHERE Category='" & category &"' AND State='" & state &"' AND County='" & county &"'"

the way the database is going to be set up now what I need to do is search through one table that will have all the states, counties, category, and UserID fields.Then it has the other table that will have a UserID field and an email field.So I guess it needs to go through the first table and depending on what state, cat, county were selected it will take that UserID and match it to the UserID in the email table and then pull the emails that match UserID.UserID? Would this use JOIN? UNION? How would this be done, to take the form info and search the one table and then depending on what userid matches the state, county, and category in that table it matches that userid to the userid in the email table and pulls the emails from the email field.