Often, when you move you will need a moving and storage company. Sometimes, you will move into a temporary home and need a place to store things until you find your permanent place to live.
Storage facilities are convenient locations to keep your extra stuff. Most moving companies offer storage services as an option. If it's just for a few days, they will usually store your belongings on the moving truck they use to move you. For any length of time longer than that, they will transport your goods to a storage facility.
You will pay for the storage facility you use on a monthly basis. The fees depend on the size of the storage unit you rent. If you are looking for a local storage place to keep your extra stuff, your moving company can probably help you find one.
If you are not moving, you can still take advantage of a storage facility. You can use it to store out-of-season items and clothing. You'll have access to the unit any time the facility is open, so you will always be able to get to your stuff when you need it.