Maintaining a sourdough starter is simple! How often you plan to bake will dictate how often you need to feed your starter and how much time you will need to spend maintaining.
When you are baking regularly (once or twice a week)
You will want to feed your starter consistently to keep it active and ready to make bread. This means that you should be adding flour and water to your sourdough starter at least once a day...twice a day if you want your starter to be more active and bubbly!
When you bake less regularly (once or twice a month)
Seal the jar that you keep your starter in and keep it in the fridge! A few days before you want to bake, take your starter out of the fridge and let it come to room temperature. If a brownish liquid has formed on your starter, don't worry, that just means they're hungry. Pour off the brown liquid and then feed your starter with flour and water twice a day until it is actively rising and falling throughout the day. You're ready to bake!
When you don't know how often you will be baking...
Take a bit of your starter, put it in a sealed container and keep it in the freezer. Follow the same steps as above to re-activate your starter and you will be ready to bake!