It would depend on the herb or plant... the uses vary widely! A great book on each plant and herb is Cunningham's Encyclopedia of magical herbs. Big ol' green book chock full of quick and easy refrences.
and as for candles- the more antureal the better. No need to be burning carcinogens and inhaling them... most chemical type candles also have a lead filiment wound into the wick. And Beeswax just smells good.
Cunningham's Encyclopedia of magical herbs is a good reference book on herbs and their magical abilities, but it will not tell you how to make a potion with them. To learn how to make potions and spells read Spell Crafts, Creating Magical Objects by Cunningham and Harrington. Remember though that they refer to potions as "potpourri". Now if you want to know the healing properties of herbs I suggest the Encyclopedia of Natural Medicine by Murray and Pizzorno or New Choices in Natural Healing by Gottlieb.
As for candles bees wax is best, soy is good too, but in a pinch any candle will do.
Mint is good for the stomach. Strawberry leaves can be put in a bath and it helps the skin. Cinnamon can be used as a bug repellent. Mugwort is supposed can be worn for attraction.
If you make an even cross(+) of oak bound with red string it is supposed to be good for protection.
American Indians have used plants and herbs for generations. You would most probably get a more specific answer if you did not ask such a general question. Is there a specific herb your are most interested in? Specific outcome you are looking for? If you would like to PM me I would be happy to provide answers to specific herbs and plants.
Plants have spirits too and it is a aspect of the plant which may be more usefull than it's actual medicinal or magick use, plant spirits if approached right can teach and guide you to the point where you do not need to use them to create their special effect, approach everything with enough respect and it will give you the assistance you require.
....and then after aquiring Cunningham's Encylopedia of Herbs book, I'd recommend The Master Book of Herbalism by Paul Beyerl and then purchase Herman Slater's Magickal Formulary Spellbooks.
The Magickal Formulary
and
The Magickal Formulary Spellbook II