The best advice for the novice gardener is to start small; a well prepared small garden will yield plenty of produce or ornamental beauty. As skills and confidence grow, gradually increase the garden's size to fit your time and energy commitments.
Buy a pane of glass that is 1/16 in (1.55mm) smaller that the window opening on all sides. Chip out any old putty. Clean out the recess, and paint it with primer. Lay a bed of fresh putty in the rabbet in the window frame. Press the new piece of glass into position around the edges – not in the center, where it could break. Insert glazing brads or clips to keep the pane of glass in place.