Once a column is set to Auto Increment the value would Increment by one for every record added. Therefore, the column value for each record would be unique and hence it could be set as a primary key. There may be times when you would want it to Increment from a specific value. This is how it can be done-
ALTER TABLE table_name AUTO_INCREMENT=1001;
In the above example, Auto Increment would begin from 1001 rather than 0.