MySQL joins allow you to combine data from multiple tables by linking related records together, enabling you to return columns from more than one table into a single set of results. INNER JOINs return only matching records between tables, while LEFT and RIGHT JOINs return all records from the left or right table, respectively, even if there's no match in the other table. FULL OUTER JOINs return all records from both tables, but are not supported in MySQL; instead, you can use a UNION of LEFT and RIGHT JOINs with a WHERE clause to filter out matches. Understanding how to use these different types of joins is crucial for performing powerful and efficient queries in MySQL.