Potentiation is when two substances are taken and one increases the strength of the other, but does not change its property. Synergism is when two substances of similar action have a net effect that could not be achieved by taking each substance separately. For example, liver herbs can synergize to create therapeutic effects that cannot be accounted for in each individual herb. Taking grapefruit juice before certain medications will make their effects way stronger but not necessarily different, so grapefruit juice potentiates medications.
There is also synergy within single plants that modern science does not account for. If you isolate one chemical in a plant, extract it, and concentrate it at many times its natural amount, and then do biomedical tests with it, the results of those tests are not going to be a reflection of how that chemical would behave if the whole plant was used as a medicine. In modern medicine they call the chemical extract the "active ingredient", but traditional herbalism does not care about this and in fact believes that once you remove a chemical in isolation it no longer has the same function. This flawed approach has been the reason for herbs getting banned, such as comfrey.
Wikipedia is actually the worst source to consult about herbal medicine because pharmaceutical shills and very pro-science types constantly delete and downgrade statements of their therapeutic values based on the above testing methods, or for completely arbitrary reasons. I can't count the number of times that the extremely beneficial effects of certain plants are not even mentioned, while at the same time are referred to as "folk medicine". There is a lot of condescending language on Wikipedia about many herbs, unless of course those herbs have been appropriated by modern medicine and turned into pharmaceutical drugs.
Just keep in mind that whenever you research herbs online there will be competing interests. The natural health industry (worth billions now) will heavily promote herbs without any attempt to differentiate who should be using them; while on the other hand, the pharmaceutical industry will make false claims about their dangers and use condescending language like "folk medicine" to defame the herbal profession. That's why I recommend books over websites.
I'm part of several herbal communities online but regrettably I cannot share them here because I don't want them to be invaded by harmful forces. Here are some books I can recommend:
Anything by Michael Moore
Anything by Stephen Harod Buhner
Anything by Eliot Cowan
Anything by Susan Weed (the Wise Woman's Herbal is a classic)
Anything by Matthew Wood
Thomas Bartram's Encyclopedia of Herbal Medicine
Practical Herbs by Henriette Kress contains accurate information on all the basic single herbs that any aspiring herbalist should know about. I think she also has part II out now too.
The Herbal Medicine-Maker's Handbook by James Green teaches you the basics for turning herbs into medicine (salves, tinctures, ointments, bath stuff, etc.) and also gives a primer on the most common 30 herbs you should look into. I think this book would be my #1 recommendation. He also authors "The Male Herbal" which is great for men.
The Peterson brand field guides based on your region in the world are also handy, and have nice photos.
All of those should be plenty to get you started. Of course, none of these are a substitute for an experienced herbalist going out into nature and teaching you about plants. If you can get first hand experience then that would be way better because you will connect to the plants directly.