A humidifier adds moisture to dry indoor air. The XL is the larger-tank version, and it runs filter-free, so there is no cartridge to buy on a schedule.
The cleaning routine, which is the whole game: Every day: pour out whatever water is left, wipe the tank dry, and refill with fresh water. Do not top up standing water.; Every week: clean and descale the tank and base using the vinegar or bleach method set out in the manual, at the dilution the manual gives.; After a deep clean: let every part air-dry completely, ideally a full day, before you fill it again. Standing water sitting warm in a tank is what causes trouble, and a daily empty is the routine that deals with it.
Water: Distilled is the recommendation. Tap water carries dissolved minerals that stay behind as scale in the base and as fine white dust on nearby surfaces. Distilled water leaves less of both and cuts the descaling down considerably.
Essential oils: On the diffuser pad. Never in the water tank. Oils in the tank attack the plastic and the internals, and that damage is not a warranty matter.
If it leaks: Switch it off, empty it, and check the tank is seated square on the base, the cap is tight, and you have not filled past the fill line. Then check the manual before you run it again.
Runtime: How long a fill lasts depends entirely on which mist setting you use and how dry the room is. Match the setting to the room rather than running it flat out by default.