Hi Linda,
I also make this and you are correct. You make the starter with:
1 cup sugar
1 cup milk
1 cup flour

Place in a ziplock bag and squeeze it every day for 17 days, on day 18 do nothing. On days 19,20,21, sueeze. On day 22 add 1 cup sugar, 1 cup milk,and 1 cup flour and sqeeze. On days 23,24,25,and 26 squeeze. On day 27 add 1 cup sugar, 1 cup milk, and 1 cup flour and squeeze well together. Now bread is ready to make.
Proceed with your recipe.
I hope this helps you. If you need more help or would like to know the flavors I
make, let me know!