I'll let you in on a secret. I have never created my own sourdough starter. We inherited ours from a friend. Once you have one it can last you a lifetime as long as you keep it fed.
It is very easy to make your own. Some add yogurt or milk to get the live cultures going. But you can get going with just flour and water.
Bread Flour (any type will do but I would recommend organic)
Add 1 cup of water and 1 cup of flour to a clean medium size kilner jar. If you don't have a kilner jar any medium size jar will do. Our starter started life in large jar that used to contain a well known brand of mayonnaise. Mix the the flour and water together with a spoon and then leave the jar in a warmish place (not too hot) covered with a tea towel.
The next day stir in another cup of flour and another cup of water. Repeat this every day until the jar is around 3/4 full. After a few days you should start to see the mixture bubble, indicating that the wild yeast is starting to become active and multiply. Once you have a frothy mixture your starter is ready to be used.
As I only use my starter around once a week I store it in the fridge with the lid on so it only needs feeding about once a week. As I also make a loaf about once a week this is the perfect time for me to feed my starter. I use the amount I need for my loaf (usually 150g) and then top up the jar with 1/2 cup of flour and 1/2 cup of water. Often when you come back to your starter after a week you find a layer of liquid has formed on top. Just stir this back in before you use your starter.
Even if you don't use the starter it will still need feeding once a week. Just tip a little of the starter away and top up with fresh flour and water. If I am using my starter more regularly I will leave it out of the fridge at room temperature and top it up every time I use it.