To answer the question, the base plate is the typically the first piece that goes on the ground that everything else is attached to. I say typically, but you have 2 beams that take that place. If it was a metal shed, that would be a different story.
In your case, the base plate is the bottom plate that sets on the floor of the shed, it is continuous on all sides except where the door is. Usually the tie downs are connected to this before the siding goes on. The corner posts are also a strong point of attachment too.
Many jurisdictions in the US do not require a permit for a small shed as yours. If the permit is needed for a homeowners association, the requirements are such that the only concerns are how it looks.
If that is not the case, and anchors are truly required, the anchors you need are pretty much a deformed steel rod, 30-40" long driven into the ground, and made so it can be attached to the outside corners of your shed by screws or lag bolts. Perhaps even a cable or two.
If this is an option, because of aesthetics, a hole can be drilled into the floor of your shed in the corner and the rod driven through the hole and screwed into the corner post.
This is a sample of anchor they will be referring to. This type can be twisted into the ground on the 2 outside corners you need, there will be 2 extra... Get the eyelet close to the ground, tie the supplied cable to the shed at the floor framing and twist the rod into a little farther to tighten it a little more. It could still be done from the inside, it would take a 3" hole to go through and tied to the corner post from the inside.