If you have a Customer Table (with columns CustKey, CustFirstName, CustLastName) and an Address Table (with columns AddrKey, CustKey, AddrLine1, AddrLine2), to get all fields from both tables, you would write a query like this:
SELECT * FROM Customer INNER JOIN Address ON
Customer.CustKey = Address.CustKey
This statement would return the fields: Customer.Custkey, Customer.CustFirstName, Customer.CustLastName, Address.AddrKey, Address.CustKey, Address.AddrLine1, Address.AddrLine2.