Quick UV unwrap tutorial
O2PE includes an unwrap function (Surfaces → Unwrap Structure …) which should work pretty good an simple structures.
I use it this way:
Select the structure you want to unwrap and change to top view
Open a UV-editor
Select “Unwrap Structure …” function and reselect you complete structure
In the UV-editor select “planar mapping” (tab-key) and select copy afterwards
In the O2 window select undo to undo the “Unwrap Structure …”
In the UV-Editor select paste to regain the UV-mapping
Now you should have your structure more or less correct UV-mapped, you only need to move the UV-maps, so they do not overlap.
On more complex structures, use professional modeling software which has good UV tools.