Centering is an energetic practice. When we center ourselves we gather our energy, which may be scattered in many different places, and we harness it toward our intention.
For example, if you are about to give a speech, you may find yourself nervous and scattered. Your energy may be focused on what other people will think of your speech, or it may be connected to a person you had an awkward encounter with yesterday, or it may be at home fussing over your convalescing pet rabbit, or all of the above and much more. Where your thoughts are, your energy is. By Centering your energy, you recall all that extra energy floating around and bring it to the center of your being and focus it on what you have to do right now: give a speech.
Centering is an important skill that is often taught early on to students of magick because it allows us to be fully present in our magickal workings, reducing the likelihood that they will be contaminated by outside energies and concerns, thereby increasing their effectiveness and safety. Magickal techniques for centering vary.
Centering is often combined with grounding.