A tincture is an alcoholic extract of herbal constituents.
To make a tincture, fill a wide-mouthed jar with the herb you wish to extract. Fill it with very high proof alcohol, seal it tightly and forget about it for a few months. The strain and re-bottle. Usually, the dosage is just a few drops at a time.
You can usually find 80-100 proof Vodka wherever liquor is sold and this will produce a very nice tincture using most fresh or dried plant material. Vodka is nice because it doesn’t have a lot of its own flavor so the herbs you are using can really shine. Brandy is also a nice choice, but it has a much stronger flavor that I like to use with sweet herbs.
If you need to dissolve resins or gums, you will need a higher proof but you may have trouble finding stronger alcohol. Everclear is an old standby that may be available at specialty liquor stores but new products such as Extractahol and E.O.X. (Amazon Links) are specially marketed for extracting essential oils and resins. Be careful when you choose a product that you are choosing food-grade ethyl alcohol that has not been denatured if you are going to be using your tincture internally. Rubbing alcohol and denatured grain alcohol might be okay for making house cleaning sprays or even muscle rubs, but they should not be ingested.
An acetum is commonly called a vinegar tincture.
Detailed directions for several methods for making your own tincture can be found at https://blog.mountainroseherbs.com/guide-tinctures-extracts