Sourdough is nothing but fun to work with! It's a living organism that you can make a variety of items with. There's few different ways to get started with sourdough... let's look...
1. Make one using a standard formula. This is the basic...
2 cups flour, 3 tbsp sugar, 2 cups warm water, 1 envelope yeast. Combine in either a glass or plastic bowl (never stainless). Let ferment for 2-3 days, stirring several times each day. Refrigerate.
2. Make a better starter. Starters being alive and what not, I like to create them with live yogurt cultures. Many people use milk and not water in their starter because the flavor is better.
2 cups flour, 1/4 cup sugar, 1 cup organic plain (not vanilla) yogurt with live cultures, 1 cup milk (not non fat). Let ferment for 2-3 days, stirring several times each day. At the end of the 3rd day, feed again, 1/2 cup flour/ 1/2 cup milk. Refrigerate.
What's the difference? You'll get better 'action' out of the first one sooner, but the flavor won't be as good. The second will take a while on the action but the flavor will be better sooner. Both starters will take 6-8 weeks to get pretty good flavor if you only use them once a week. Longer if you use them less.
3. Get a starter from someone else who has one. This is where the theory of the older the better comes into play. The one I'm currently using is around 160 years old.
To make additional starter... if your making something that calls for two cups of starter instead of adding 2+2 (2 cups milk, 2 cups flour) add 3+3. Give the extra cup of starter to someone else and let them play with it!
Care and use of your starter. Mine thrive when I use them once per week. I've ignored them for a few weeks and had them be okay. If they separate and get a clear layer of liquid on top, just take it out and feed it. Likely it will be okay unless it's been a year since you looked at it! Starters can and do die, but it takes serious neglect.
If you're intrigued by the slow food movement, you'll love this! If you occasionally have time, you'll love this. If you love instant stuff, this might not be for you as you definitely have to think ahead a little for sourdough!