The top face is the one that should be forwards when cutting.

Yes, just sharpen the top surface of a typical form cutter. Don't overdo it and take care not to round them over or it will rapidly heat locally, wear and go blunt.

The 10 degree relief is to stop it fouling the work, typically it will be set slightly back from a diameter of the cutting circle to provide a small amount of top rake, but not much otherwise the shape of the cut will be compromised.

That on the bottom is for the same reason and may or may not be needed depending on the overall geometry.

It's all easiest to understand once you have made the first cut and can stop the machine and offer the cutter up to the work. It should then all become clear.

I've found this sort of cutter to work surprisingly well even in steel, if used with neat cutting oil and not worked too fast.

Neil

As Neil mentioned the extra cut away underneath is for clearance. When you mount it in its arbor note the radius and find something or draw/cut a hole to match. Then offer this up to the cutter and make sure it really is clearing.

This is something similar that can catch you out when boring a small hole where a bit of the tool away from the cutting edge fouls the bottom of the hole and messes things up before you twig what is going on.