Buy a jack plane and a sharpening stone at a car boot and learn to use that. Go easy on the learning curve then follow the advice above to finish it off. Oak is about as hard as any wood in normal use certainly few boards are harder. Practice planing on some softwood then set the plane to as fine a cut as you can.
It will skim along until you have it good enough to sand. You won't be digging clumps out of oak. But start with 120 while you learn.