I noticed that there were a couple of recipes for starters here, but I want to add mine because I have used it for over 40 years and I really like it! And so easy to make.
This is the old way Starter was made by settlers and by the cooks on the trail. I think it tastes the best
Boil potatoes (I use Idaho russet potatoes) take the warm water after removing the potatoes about 2 cups
Add flour to make a thick batter.
Let it stand a day or two until it smells right and is bubbly.
Refrigerate in between bread making times. Remove from the fridge several hours in advance of using it. You will see it start to bubble and grow in the container. Once it is active use the amount called for in the recipe and then replenish the starter. Use warm water and flour to make batter and add to the starter. Let it sit until it starts to show activity and is bubbling and growing and then you can store in the fridge.
Use a glass or ceramic container, putting cheese cloth over the top is good way to store.
Good luck with your starter and may it last you years!!