Finally, let's look at how you delete data from your table. Note that when you delete something from MySQL, it is deleted - gone, no more, etc. Unless you use transactions that aren't committed, there is no "undo" feature. This is inherent to all databases, not just MySQL.
Here is the most basic way to delete data from a table:
DELETE FROM usertable;
That will delete all rows from a table, in the say way "SELECT * FROM usertable" will select all rows from a table. DELETE takes both the WHERE and LIMIT clauses, allowing you to construct more complicated statements such as this one:
DELETE FROM usertable WHERE FirstName = 'Bill' LIMIT 3;