Self watering, or wicking pots are great when it comes to growing annual vegies. The water is delivered to the roots of the plants, so less loss to evaporation with overhead watering as well as helping avoid fungal issues that can happen with water left on the leaves of the plants.
This DIY version has a reservoir of water at its base, held amongst a mix of small gravel pieces and some sand. The potting mix is held above this by a layer of mesh that helps keep the layers separate. Watering is done through an inlet pipe that you would insert before adding soil and there is an outlet pipe to make sure you can't overwater.
Try one yourself and you'll notice the difference compared to standard pots.