The % you see advertised is the %of Nitro in the fuel. Most engines run well on between 5 to 15 %nitro content. Check the engines manual for the reccomended Nitro.

After run oil is a protective measure to prevent your engine from rusting if it's going to sit for a while. Since methonol tends to draw moisture from the air. ( methonol is also an ingrediant if glow fuel.) A couple drops of after run oil after each day flying is a good habit to get into.