Rain Barrels are simple. A plastic, food grade barrel, a measuring tape, a jig saw, two spiggots, a basket for debris, and a drill with appropriate bits are all you need to build your own.
Once your barrel is clean, drill a hole near the top of the barrel and one near the bottom of the barrel to fit your spiggots. Wrap the spiggots with plumbers tape. You will use the top spiggot as an overflow. Connect a hose and direct it away from your foundation into an area that the water can slowly permiate into the ground. Or you could connect the hose to another barrel to fill.
You will use this spiggot to fill your watering can, connect a watering hose or a soaker hose.
Measure the size of your inlet basket and cut a hole in the top of your barrel to fit. You will aim your downspout to drain into the basket. The basket will collect any debris from your roof and gutters.
Drop the debris basket into the top and you're ready to go.