"Herbs" is a catchall term, commonly used in reference to any plant substance such as bark, root, leaves, resin, flowers or stems. Often they are used in incense recipes, in mojo bags, ground and sprinkled as powder, or hung in bunches. Some herbs are used as tea, for a combination of medicinal and magical purposes. Since essential oils have the same purpose as their source herbs, I will only list those herbs which are used solely in herb form, or have medicinal value.
Acacia: Stimulates psychism
Adam and Eve Root: Useful for spells to get married or heal a broken marriage
Asafoetida: Use sparingly in exorcism and banishing incense and powder
Balm of Gilead: Burn to cause spirits to appear
Bear Berries: Carry to increase psychic abilities
Black Snakeroot: Carry for courage
Buckthorn: As a tea, makes an excellent cathartic
Copal: Used in image magic to represent your target's heart
Damiana: As a tea, acts as a mild aphrodesiac
Dittany of Crete: Burn to cause spirits to appear
Fava Beans: Also called Mojo Wishing Beans
Hand Root: Used in mojo bags for good fortune, especially six-fingered
Hyssop: As tea, oil, or incense, used universally for purification
Jalap Root: Carry to increase power and courage
Job's Tears: Wish on seven of these, and throw them into running water
Mandrake: Either may be used in image magic
Male Mandrake: Used to stimulate one's personal power
Female Mandrake: Kept in one's house for protection and good luck
Orchid Root: Carry to attract love, or powder and sprinkle on the object of your love
Orris Root: Used in mojo bags to attract and keep a lover
Patchouli: May be used in some cases where Graveyard Dust is called for
Raspberry Leaf: As a tea, used by some to relieve menstrual pain
Tonka Beans: Wish on one, and throw it into running water
Yew: Bury a wand of Yew in a grave for one full moon to raise the deceased's spirit
Many practitioners of magic using traditions like to use scented oils. Oils are either "essential" (pressed or extracted from real substances) or "fragrance" (substitute or synthetic scents). The essences on this list may also be used in whole-herb form for the same purposes.
Allspice: Used in money sachets and incense
Catnip: Good for psychic bonding with feline familiars
Cinnamon: Burned as incense, or used as anointing oil, to stimulate spiritual power
Clove: Attracts the opposite sex
Frankincense: Burned or used in anointing oils for purification and power
Galangal: Used in anointing oils to stimulate spiritual power
Jasmine: Stimulates psychic powers, and also induces sleep
Lavender: Used to induce sleep, also attracts men
Lemon Verbena: Attracts the opposite sex
Lotus: Stimulates spiritual power
Mastic: Burn to cause spirits to appear or stimulate psychic powers
Mint: Used in mojo bags to attract wealth
Mugwort: Rinse scrying devices with an infusion to activate them
Myrrh: Used as an oil or incense to consecrate altars or ritual tools
Rosemary: As oil or incense, used to purify a space
Saffron: Drunk as an infusion to become prescient
Vetiver Root: As oil or incense, use to break hexes
Wormwood: Burn as incense to increase psychism
Precious and semi-precious stones and crystals are very important to many magic-using traditions. Often they are used as amulets and in mojo bags.
Amber: Amber absorbs the vital essence of its owner. Amber is good for generating powerful solar energy.
Amethyst: For clarity of mind. From the Greek "A Meth"--"without drunkenness"
Bloodstone: For physical strength and health, closes wounds
Calcite: Amplifies one's magical energies
White: For use in meditation, adds focus
Pink: For calming and balancing the emotions
Blue: For healing and purification
Green: For prosperity and wealth
Orange: For protection and power
Jet: Like Amber, Jet absorbs the vital energy of its owner. Amber is the blood of the earth, while Jet is the body. Excellent for physical robustness.
Moonstone: For divination and psychic enhancement
Onyx: Protection and "cloaking"
Quartz: A natural generator. Quartz crystal is excellent for powering amulets with unbiased energy.
Obsidian: An excellent stone for scrying mirrors and also for protection. Arrowheads of obsidian are especially powerful
Pyrite: Although "Fool's Gold", Pyrite is commonly used in spells to attract wealth and prestige.
Ruby: A deep red jewel, the Ruby is very potent with Mars energy. Ruby is excellent for protection and personal power.
Sapphire: Sapphires are good for psychic ability, especially telepathy. Sapphires are also rumored to protect the health and heart.
Star Ruby: A beautiful stone with a six pointed refraction inside, the Star Ruby is associated with Chokmah, the Supernal Father, and the universal Masculine.
Star Sapphire: Like the Star Ruby, the Star Sapphire is a deep rich color ranging from bluish to a dark grey, with a six pointed refraction inside. Associated with Binah, the Star Sapphire represents the Supernal mother and the universal Feminine.
Sunstone: Power and protection, solar power
Tiger's Eye: Courage and strength
Topaz: Draws wealth and protects against accidents
Blue: Cools the body, worn next to the skin
Gold: Warms the body, worn next to the skin
Pink: Draws love and friendship
Red: For protection, will and courage (rare)
Green: Draws money to wherever it is kept
Blue: For peace of mind, or to induce sleep
Black: For absorption of negative energies
These are some of the components commonly used in practical magic. Learn them well, not from any list but from your own experience. Books are well and good, but only as springboards--your best magic will come not only from within, but with time.