Chalkboard paint is simple, and just like using regular paint. Before using it, sand the surface to make it smooth and help the paint stick. Next, with a ruler and a level, measure the area you wish to chalk paint and then mark off the space with painter's tape.
There are plenty of cool colors of chalkboard paint in the craft stores. There's also spray paint, but it requires a well-ventilated area for safety's sake. If you're using the canned chalkboard paint, paint the corners and then roll the rest with a low-nap roller.
One idea is to make a growth chart with chalkboard paint. Paint some trim pieces red and use them to frame the chalkboard part of the wall, attaching them with finish nails. Then run a self-stick measuring tape down the length of the chalkboard, so you can use it to record your child's height over the years -- writing with chalk, of course. Start the measurements from the floor, not from the bottom of the chalkboard.