Novice MySQL problem

Hi, I'm a novice to MySQL and am currently facing the following difficulty. I'm trying to update a table with a row of data the primary key of which is an ID which I believe is an auto incrementing serial number. My first question is how to check if this is the case. Secondly while trying to insert such a row leaving out this column mySql is inserting the row at ID 0 (the previous ID's in the table are from 1 to 9), but then will not take further inserts. Thanks for any help available. Regards Toni