Now that you have learnt how to update and delete records in your table, it is only really a matter of time until you issue your first query like this:
UPDATE usertable SET FirstName = 'Bob';
Then realise you meant to add "WHERE FirstName = 'Robert'" at the end. Instead of changing Robert to Bob, your query will also change Peter, James, Sally, and anyone else in the database to Bob - a disaster!
To work around this, the MySQL monitor has a special command line option, --i-am-a-dummy (seriously, it does), that will, amongst other things, not allow you to execute any UPDATE or DELETE statements without a WHERE clause. This might sound a bit extreme, but you will be thankful for it if you issue wrong queries regularly!