If the tables are related you must use JOIN: let's see an example (I don't know your tables fields, so I'll invent a custom example). Think about person and pet tables; the person tables could contain these fields:
Person (personID, first_name, last_name, age)
the pet table could contain these other fields:
Pet (petID, name, age, personID)
The personID field in the pet table identifies the owner of the pet. It is a simple 1:N relation. To select some values from these two tables you must do something like:
SELECT Person.first_name, Person.last_name, Pet.name
FROM Person INNER JOIN Pet ON
Person.personID = Pet.personID
WHERE Person.age > 30
This is just an example, clearly. And the INNER JOIN is just a join type (there are several join methods). Here you can find some documentation concerning these issues.