[whpalmer4]

You can simply copy and paste from a text file if that's where you already have them. Just make sure when you do the pasting that you have an entire row in the outline selected (clicking on the row handle is one easy way to do that) or the whole mass will be entered as one row instead of a row for each line in the source.

OF will also import an OmniOutliner document. Use File->Import to select the OO document, and then you'll get a little popup window that allows you to map which column goes where. Unfortunately there is no "bit bucket" to accept unwanted data, so you'll want to get rid of excess columns (if any) before the import.