You can consume them any way you like, but I believe they are intended to be used directly onto or under the tongue for maximum effect
One of the main benefits of tinctures in general is that they can be taken orally/sublingually, in which case the active cannabinoids are absorbed directly in to the blood stream and distributed throughout the body that way. This is a much faster route of administration than other edibles that have to be digested and processed by your stomach and liver before being distributed to the rest of your body.
If your condition does not require fast-acting relief you can definitely consume the tincture any way you like by adding to a drink or food. At Sessions we sell coconut oil-based tinctures that are great for this! Just keep in mind this will delay onset of effects.
For fastest onset, try dropping the tincture under your tongue, holding it there for 5 to 10 seconds, and then swishing it around a bit before swallowing. This will allow some of the active cannabinoids in the tincture to be absorbed directly through the blood vessels in your mouth which means more rapid distribution to the cannabinoid receptors throughout your body.