Top surface is just what it says. The difference is that this layer is dictated by your set layer height. Assuming .3 which is normal you would get a top surface layer that is .3mm thick on each pass. For .3 two or three layers are common. For a lower layer height that might need to be raised if you notice gaps in your top surface.

Infill is what it feels the empty space with and is usually a percentage. This is what gives your part strength. For structure parts that need to handle loads you would 50 to 90 percent. 90 percent is usually solid enough for any pupose the mateial can handle. If it is a figure or just a rough test print you would use less than 50 percent to conserve filament. Of course this also depends on thr depth of your pockets. If cost was no issue then I guess you could print everything at 100 percent infill.

What do these options mean? I really have no idea how many layers to assign to each one and what they specifically do for the print. I also see you can adjust the speed for each shell category... not sure whats up with that either... Can someone fill me in? Thanks in advance.