The best way for me to visualize the relation between wavelength, frequency, and energy is to think about actual ocean waves. Wavelength is a measure of the distance between two equivalent points on consecutive waves (think wave peak to wave peak). Lets say you are building a sand castle and want to see how many waves hit your castle over a period of 10 seconds. If the distance between each wave is 10 ft and the wave is traveling at 1 foot per second then you will only have one wave hit your castle. If the wavelength is 1/2 that (5 ft) then you will have 2 waves hit your castle in the same amount of time. This is the same concept behind waves in physics. The smaller the distance between each wave, the more waves and therefore more energy that will be delivered.
So you subtract the numbers that are on the same axis. So if your gravitational force is 10 and your normal force is 5 you do 5-10 to get -5 since gravity acts downward
