Sometimes an herbalist will call an extract made by extracting herbs in vinegar or glycerin a tincture but usually the vinegar is called a tinctract or vinegar extract and the glycerine extract a glycerite. Generally when an herbalist says the word tincture they are talking about an herbal extract made with alcohol or alcohol/water.
Making herbal tinctures can be quite easy or very detail oriented and involve a lot of math depending on if you want to be exacting or not. The easy method of making tinctures called the folk method is a system that many beginning herbalists use.
If you want to make a tincture that is the same strength each time, you need to use a bit of math and follow a formula to ensure you make the product the same each time. Herbal companies use mathematical formulas to make sure they have consistency. Many herbalists do also.
The Folk Method of Extraction:
In the pure folk method people often don't take into consideration the percent of alcohol the plant would be best extracted with. Often people use whatever they have around and it is often something that is 80 proof or 40% alcohol. Fill the jar about 1/3 -1/2 with fresh or dried plant material. Pour alcohol over the top of the herbs. Realize that the herbs will soak up the alcohol so you may need to add extra later. You can check the next day to see if you need to add more alcohol. The alcohol must stay over the top of the plant by at least 1/4 inch at all times to keep it from oxidizing. If you are adding alcohol to fresh plant you won't need to add more due to their being water in the plant. With the dry plant extract, the plant will suck alcohol into its dry cells. This is why you have to add more later. If you are adding alcohol to dry plant, you will definitely need to add more the next day. Put a lid on the container and steep for 4 to 6 weeks in a cool, dark place such as a pantry. Shake it often. Then strain or press out the liquid or menstruum. Usually in the folk method you don't even both filtering it. You simply use as is. This is really all there is to the folk method. It is very simple and you don't have to know much to do this. In many cases this will work just fine.