So easy. First you need a crock or non-reactive bowl, 3 qt or so. I use and old "crock pot" crock and for a cover I use a plastic shower cap. NEVER make starter in a tightly closed container, because as it ferments the gasses will blow the top off! Start with 3 C. warm Water - 110 - 115 deg. Add 1 1/2 Tbsp. of dry Active yeast, 1 Tbsp Sugar and stir all together; wait till the yeast gets foamy, around 5 minutes. Add 3 C. Bread Flour and stir in well. Cover with the shower cap and let it set on the counter for a couple of days. Stir every now and then. After four days, refresh the starter by stirring well and removing one cup of the starter. Add one cup of flour and one cup of warm water and stir in. I let mine work on the counter for a week or so to get it to point of sour that I like. Refrigerate after that and refresh once a week...Leave out overnight after refreshing, then refrigerate again.
When you use it, replace the amount you take out by the same amount. I also add a teaspoon of yeast now and then, although some others may not agree with that.
Let me know how it comes out for you.