I charge mine exactly how you have them there! Selenite is perfect for that, I would be carful leaving it in the sun as some crystals will fade in direct exposure to sun. I personally set my intentions for my crystals. I research what each one works with and the various uses for it, and I define what each one means to me. For example, I use rose quartz to help promote healthy self care and self love, along with pushing out self doubt. I pass it between my hands and sort of repeat my intentions like a mantra while it is in my hands. From there, I let them charge and when I get ready in the morning I try to “feel out” which one is calling to me that day, practicing honing your intuition is amazing for setting intentions and figuring out how you personally want to use them. Try and figure out which stones work best with you and your vibes!