The Field Type is the type of field that will be created in the MySQL table. If in doubt, just leave this with the default Text, which can store just about anything. If you want to ensure your database is as efficient as possible, you should select the appropriate data type. For example, if your options are yes and no, you will only ever store a maximum of 3 characters so varchar(3) is going to be more efficient than Text. Unless your database is really big or under a large load, you probably wont notice any performance benefit. Another example is when you only want a numeric input, you might select INT as the field data type.