Crystals channel the energy levels in your body. Much like how the vibration of a tuning fork can be influenced when we touch it, crystals can influence us. Your crystals can also be influenced by you, so it is a good idea to regularly “charge” them; or reset their vibrations. This can be done in a number of ways including playing loud music, putting them in moonlight, or placing them with a piece of selenite/satin spar.
Selenite is a never ending battery: it will charge your crystals and never needs to be recharged itself! A simple way to do this is by putting your crystals into a bowl, and placing selenite on top. There is no set amount of time or frequency in which you should charge your crystals, it is all personal preference.
Do not put selenite in water, it may dissolve or fall apart and cause splinters to form which could irritate your skin. If you desire to wash your selenite, use a slightly damp paper towel. Be very careful not to get slivers into your skin. You may wish to do this outside while wearing gloves in case any pieces come off.
(Further care tips can be found here)
Selenite, desert rose, and satin spar are types of gypsum. They are made of the same things, they just crystallized into different shapes. A lot of people use selenite and satin spar interchangeably, which isn't a bad thing. Gypsum is the species, the others are the breed. A golden retriever and a chihuahua are both still dogs at the end of the day!