On the screenshot below you can see how table editor looks when you create a table with MRG_MyISAM storage engine.
Select preferable method of inserting data.
First - inserts will be made in the first table.
Last - inserts will be made in the last underlying table.
No - no inserts to the table allowed.
Select first table for union
Select a table from the drop-down list. This selection affects selection of other tables for union.
Select other tables for union
This section contains the list of tables identical to the first table. “Identical” means that all tables have identical column and index information. Mark tables you want to include in union.
For the description of common options refer to the Setting storage options page.