Do not grief the server. There are many ways to do that, but the most common are to intentionally crash the server, lag the server, destroy or damage the spawn, destroy or damage other player's builds, erase warp points, PVP without agreement of other players, chat spamming, and so forth.
Use your best judgment, and remember that other people are on here to have fun also.
To save your builds (i.e. create a WorldEdit schematic), first use the //wand tool to select the bounds of your build (i.e. the opposite corners of your build). Then, type //copy to place your build on the clipboard, and type //schem save nameofbuild to save your build (replacing nameofbuild with a unique name of your own).
To load a schematic back into the world, do //schem load nameofbuild, and then //paste..