The wand is one of the four ritual tools found on a traditional Wiccan altar and is used for rituals, sabbats, and to cast spells. Thanks to the Harry Potter books and movies, everybody nowadays knows about wands. Just as shown in those books and movies, the wand is used to channel, focus, and direct psychic energy.
Most Wiccan wands are made of wood, but could be fashioned from bone, stone, or metal, though some Wiccan traditions might avoid anything metal because of the aversion of most nature spirits to iron. If you want a wooden wand, consider the types of wood available and their meanings and appearances. Oak and ash are steeped in northern European folklore. Willow has beautiful associations with water and the divine feminine. However, if you live in the desert, you might love a wand made of cholla wood. Make your choice based on your intuition and attraction to a certain type of wand. This is why it is often better to see, handle, and choose a wand in person rather than to buy them online. Visit a metaphysical bookstore and supplies shop, or investigate your local pagan festival / renaissance faire.
Maybe you would like to make your own wand. It can be very fulfilling to customize your wand’s appearance. Meanwhile, the creative process itself imbues your wand with your own psychic energy. What size should your wand be? If you place your wand inside your forearm, it should measure from the crook of your elbow to the tip of your longest finger. You can leave the bark on or strip it off to reveal the heartwood. Sand the wood or leave it rough. Carve it with runes and symbols, adorn it with beads, or leave it plain. You can wrap its handle with leather or cord. You can finish your wooden wand with beeswax or linseed oil. Avoid synthetic sealers such as lacquer or varnish, which tend to stink tremendously and block psychic energy.
So how do you harvest a wooden wand from a tree? The easiest way is to look for a fallen branch, perhaps one taken down by wind or in a rainstorm. Think of this as a donation from the tree. If you wish to preserve the bark, you want a branch only a few days detached from the tree that you can allow to dry indoors. A branch that lies outdoors much longer than this will shrivel under sun and rain, lose its bark, and grew brittle.
If you cannot find a fallen branch from your tree of choice, you will have to prune the branch from the tree. First, make sure the tree looks healthy and has enough branches that it can afford the loss of one. Do not choose a tree that is too young or suffering from drought or blight. Second, honor the tree with a ritual of gratitude that includes sacred libations of water or wine. Explain to the tree why you need a certain branch. Third, prune the branch correctly to avoid tearing the bark down the tree trunk. Here are instructions that I have paraphrased and condensed from a reputable internet source, TreeHelp.com: make one partial cut at a point located on the underside of your branch and the branch-side of its branch collar (the thicker ring of bark that connects your branch to the trunk), followed by a full cut through the branch farther out, starting on its top side. The full article can be found here.