Herbs like nettle, chicory, burdock, dandelion, kale, mustard greens, and lamb's quarters are nutritive and tonic. Adding a splash of vinegar to your food helps build bones because it frees up minerals from the vegetables and greens you are eating.
Find a glass jar that you like. If it has a metal lid, the best thing you can do is cover it with melted beeswax, as metal reacts to the metal and will, in time, actually eat though the metal lid. Even several layers of waxed paper, fixed in place with elastic bands will suffice to cover while the herbs macerate.
Stuff the jar full of the herb (I've used lamb's quarters today). Best to chop it up, although I forgot to do that this time. I just used the fresh tips. in this early spring here, most of the plant is fresh. Pour room temperature apple cider vinegar (I use living cider, with the mother). Label with name of herb and date. Put it in a dark cupboard for six to eight weeks, then strain and bottle your vinegar. Some use the "pickled" herbs, others discard them.
Pour a little over cooked greens, stir fry and use as an ingredient in salad dressing. A teaspoon or so in a glass of water, hot or cold, is delicious, always refreshing and makes your body more alkaline.
Other vinegars can be made with aromatic herbs, single or in combination.