A single adult leopard gecko does well in a 20-gallon long tank at minimum, with more floor space always appreciated. Leopard geckos need a temperature gradient: a warm side around 88-92ยฐF (usually via an under-tank heater or heat mat, not just a heat lamp) and a cooler side around 75-80ยฐF, so they can regulate their own body temperature by moving between zones.
Unlike many reptiles, leopard geckos don't require UVB lighting to survive, though a low-level UVB bulb is increasingly recommended for overall health. You'll need three hides at minimum: one on the warm side, one on the cool side, and a humid hide for shedding.
Substrate should be solid and easy to clean โ reptile carpet, tile, or paper towels are safest for beginners, since loose sand-like substrates carry a risk of impaction if ingested.