This page will tell you everything you need to know about how to safely and ethically house a crested gecko.
Enclosure: Many types of enclosures can be used to house a crested gecko, options include glass terrariums, plastic bin totes, diy sealed wood, pvc and other modular types, etc. The main takeaway with enclosures is size and ventilation. Crested Geckos are arboreal, they need more height than width or length. For a single adult gecko, a 12x12x18 would be the absolute minimum but is not ideal, an 18x18x24 is better and can house 2 geckos. Not all geckos like large enclosures, babies in particular have a hard time finding food if there is too much space, so you may need to start off smaller and upgrade as the gecko grows. If you are using a bin tote or have a diy enclosure, make sure you are adding in ventilation in the front towards the bottom and on top. This allows for a nice chimney effect air flow so things don't become stagnant and moldy.
Humidity: Crested geckos need high humidity, to accomplish this, you can use a fogger, mister, hand pump, spray bottle, etc. A fogger or mister is the easiest almost hands free option, if you choose manual spraying, you must do it at least once every day. If your humidity is not holding high enough or long enough, you may need to do it multiple times a day. It's important to let the humidity rise to optimal levels (around 70-80%) and then fall back down (around 40-50%) before you make it rise again. It can't be constantly 80% or above at all times or you will be growing mold and other nasty things before you know it, and you will most likely cause a respiratory infection in your gecko.
Lighting: Geckos need a light/dark cycle to simulate day and night. They will sleep during the day so they need lights ON and during the night they will be awake and need the lights OFF. There is still much debate on UVB or no UVB, I've seen no real evidence either way. If you do choose UVB, it would only be at extremely low levels and time periods. You would also need to watch how much vitamin D3 you are supplementing.
Nightlights: Don't use a nightlight, black light, RED light, funky party light that changes colors, etc. Your gecko will not appreciate your efforts to make them look cool at night. A small time period (roughly an hour or two) with blue "night" lighting is ok, some geckos will hunt at dawn/dusk, some will not come out at all until all the lights are off.
Temperature: Crested Geckos don't like it too hot. You will never need a heat lamp or heat pad unless you live somewhere extremely cold and can't regulate the heat in your house well. Optimal temperatures are roughly 68-75 F, they can survive in cooler or warmer temps for a short period but it is not suggested that they live in those temps. Warmer temps tend to be more fatal than cooler ones. Do not let your gecko be 80 degrees or above for an extended period of time.
Substrate: There are a few options for substrate, bio active (which is a whole learning process in itself), a little bit of leaf litter and coco bark, moss, reptile carpet, plain paper towel, etc. For a baby, I highly recommend reptile carpet or plain paper towel, until they're not dumb enough to eat the substrate, for some geckos that day never comes. Never use sand or stone as substrate.
Special Bowls: Bug bowls are handy for keeping your feeder bugs from wondering off and setting up camp inside the enclosure. They also help your babies and not so bright geckos from eating substrate along with dinner.
Decor: Geckos need things to climb on, jump to/from, and hide in or under. There are all kinds of live/real or fake thinks like that you can add to fill up your enclosure like vines, plants, roots, trees, stumps, sticks, bamboo shoots, coconut hides, plastic hides, cork bark, foam pool noodles, etc. Just make sure whatever you put in the enclosure can withstand moisture, doesn't have any sharp bits or edges, and doesn't have any holes or nooks that your gecko can get stuck inside of.
Backgrounds: Some enclosures come as a kit with a foam background or you may have a diy background, always check and make sure it is sealed at all edges with silicone so that your gecko doesn't end up stuck behind it and die, you'd be surprised how small of a hole or lip they can fit through or in. Backgrounds aren't necessary in the least, they are for our visual benefit so don't let your aesthetic vision override the safety for your animal.
Lay Box: For adult females, you may want to include a lay box. If you do not have a substrate she can dig in or if you do and you are hoping to make your life easier, you can easily make a lay box out of a tupperware container, some coco fiber, eco earth, leaf litter, moss, etc and keep it moist at all times. Some females will not lay if they can't find a decent place to do so which may cause egg binding.