Legends in GRASS only exist for raster maps. Currently, GRASS does not support legends for vector maps such as those drawn with d.vect.area.
See the module d.legend for your legends. (This module is in active development for the moment, so its usability should continue to be enhanced in the near future.) You can use d.legend to display a legend in the same monitor as the map, or in a different monitor (use d.mon to start and/or select a different monitor). Through its "-m" option d.legend allows you to place and size the legend with the mouse.
Currently d.barscale is your best choice for placing a barscale on your map, including a small north arrow. If you would prefer a simple line instead of a barscale, you can use d.scale (NOTE: this is depreciated as of GRASS 5.3, d.barscale -l does the same thing, only better). However, the latter does not survive a zoom or pan, while the former does. Furthermore, d.barscale also gives you the choice of feet/miles instead of meters.