There is actually an even further distinction to make here- the difference between tea and an infusion. Tea is actually made from steeping the leaves of tea plants, white, green, black, etc in hot water. An herbal infusion is made when you steep the leaves or sometimes seeds of a herb in hot water, such as chamomile, lavender, yarrow, etc. A decoction is made by simmering the roots or bark of a plant over heat for 10-20 minutes to extract their full quality.
If you want to create a recipe that calls for various forms of the plant, for instance mixing ginger and fennel for a digestion soothing tonic, simply simmering about a tablespoon of fresh ginger in 1 1/2 cups of water(some will steam off) for about 20 minutes. Turn off the heat and add 1 tsp dried fennel, let steep for 5 minutes, strain and serve.
Do keep in mind that ginger is very stimulating to the blood, so be cautious if you have high blood pressure or anxiety. As with all herbs, just because they are not pharmaceuticals doesn’t mean they don’t have effects. Be certain you have no adverse reaction before using a full dosage and listen to your body.