Washing your brushes is quite simple. All you need is a mild shampoo and some water (I usually use a drug store shampoo I can find on sale -- I am currently using Aussie's Volume Shampoo). A shampoo is also good for brushes because you wash your hair with shampoo, brushes have hair...you get the picture!
All I do is put some shampoo and water into my hand and rub my brush in it, rinse it out, and repeat until the water runs clear (definitely not rocket science)!
IMPORTANT TIP: Hold your brushes downward. If you let water into the brush handle, it can loosen the glues holding the brush hairs into the brush, thus ruining your brush.
The ideal amount to wash your brushes is every week, but every two weeks will do too. Just don't forget to wash those babies!!!