Map Tutorial - Hex Map sub-section
Step 1 - map size
Open the Map Editor from the File menu. Then resize the editor window to how big you want your map.
Step 2 - create the Hexes
From the EditorTools menu, select one of the Create Hex Field commands, and the window will be filled with Hexes.
Step 3 - Carve away
Control-click on hexes to delete them. Having some gaps makes for a more interesting map in the end.