Here's a quick way to make oars out of two by fours and other scrap lumber. It's a lot quicker to do it than to read about it.
More paddle and oar making projects:
Here's the quickest way I know to make a paddle.
How to make an Eskimo style kayak paddle from a 2x4 in 1.5 hours
Make a steering oar for a Marshall Islands Racing canoe.
Step 1: Sharpen a Pencil in a Funny Way
Get one of those wide flat pencils from the lumberyard. Sharpen with a knife as shown so it's flat on one side and sharpened on the other side. Finish by rubbing it on a piece of sandpaper.