Easy, if you'd read the Wiki you would know though..!
Basically, find the plot of land (which you have already done.) Then start building, as moderators don't really like protecting blank areas, they wan't proof that there will be something there, even if it's just one small building. Do that first and then type in the following exactly:
/pe new Please protect this building and the surrounding areas for me to make a town.
the "/pe new" command creates a message for staff to see so that they can set about doing what you ask.
You can also use /pe open and, as far as I'm aware /pe create. These do the same thing so /pe new is fine.