Keyboard Preferences
Tab options - You can change how Tab behaves in single column and multiple column documents. In single column documents it's natural to have Tab indent the row, but you can disable this option.

Multiple column documents are more like a spreadsheet, so the default action for the Tab key is to go to the next or previous column. However, if you are used to having Tab indent rows, you can make it work the same way in both cases.
Note: You can also use ⌘] to indent and ⌘[ to outdent.

Return / Row creation options - You can change the response of the Return key when editing in a row. The default action is to leave the current row and create a new row, but you can also have it so the current row will be split at the insertion point. You can also specify whether a new row will be created at the same level, or whether it will be indented if the current row has subtopics.

Related Topics
Table of Contents: Using OmniOutliner
OmniOutliner Features
OmniOutliner's Info Panel
OmniOutliner Menus
OmniOutliner Preferences
General Preferences
Text Export Preferences
RTF Export Preferences
Update Preferences