Section View in engineering terms CAN be a section cut in half and looking at it from the inside. But a more precise definition is where you cut a line between an area which you are interested to know the internal details of. It could be wanting to know the internal arrangement of lets say.. a hollow cylinder or a screw thread
Plan View on the otherhand is indeed how we see things from the top -- think of architect drawings and the house/building plan layouts
Thread Convention, I have heard of it, but I have never bothered to understand its meaning. best to ask a drafter or something!
Hope that helps