Warding is a practice of creating protective shields or barriers around a space. The space could be stationary, such as your apartment or house, or the space could be mobile, such as your car. I would also venture to say that a protective barrier could be placed around yourself, or even a pet if you chose to do so. When I envision a ward around myself, I often think of a personal space bubble that is also energetically charged to keep certain things away from me.
Force field/bubble/shield, a ward is a protective barrier that keeps something out or away. Before warding, it is recommended to cleanse the space in order to ensure damaging or harmful elements aren't "trapped" or lingering within the ward you put up. You can read more about cleansing in this post.
Warding can be done in a variety of ways: some people create sigils or use written words tophysically mark the perimeter of the ward, or to carry the intention of the ward in an artistic form. Using a wand or other directive instrument is another option for warding, to direct and visualize the protection streaming from a powerful item. I know of people who use incense or fragrant oil/water sprays to create wards, but I personally prefer this method for cleansing a space.
Some wards might last longer than others - it depends on the situation you're warding in. If it feels like you need any extra protection, your ward may become less effective more quickly because it's under some strain. Certain stressful situations may warrant a shield. Other wards might be done at specific times on schedule, during a certain moon phase with certain significance or on the same date each month. Everyone is different in their needs, and our needs can shift.