For that Mouthwash Tincture recipe, it is saying to add the mL/Oz of each herb to make a blend (these would be tinctured with alcohol, but technically there are alcohol-free tinctures that are called glycerites, where glycerine takes the place of alcohol. These are used a lot for children, and people who avoid alcohol).
In the recipe at the bottom, I see your confusion. For the dosage, it says to add 2.5-10mL to 20mL water. The 20mL is not apart of the tincture recipe, it is to dilute the tincture a little so that people can swish it around in their mouth, like you would a regular mouthwash. The tincture on it’s own would be too strong for the oral mucosa due to the alcohol (as well as taste). So, for all herbal mouthwash tinctures, always add 20-25mL water before swishing in your mouth.