Please tell me how to start a votekick because bunch of griefers are destroyng the buildings...

1. Look up their ID on the scoreboard.
2. Using that ID, type into the general chat (using 't'): '/votekick ID' where ID is the player you want to kick.
(3. I would advise then telling the rest of the server the reason(s) for votekicking that individual).

This would more belong in the Support forum by the way (for future posts of this kind)

To start votekick you must type /deargodpleasehearmyprairsiwanttokicksomenaughtymancalled<nickname>andusingid <id> instead of /k <id>