go to http://tasks.poole.ch/job/new
    add a meaningful title
    select "Draw it yourself" or add a polygon (if it isn't too large)
    draw a polygon around the area in question (double click to exit the drawing mode, drawing a new region erases the previous). I would keep the regions to maximum city size.
    the "zoom level" selector determines how many tiles are available to be farmed out to mappers, 14 is probably a good value, in very dense regions 15 might be better
    if there is a link to imagery (other than bing) add that, otherwise hide the info
    create the job.