Little Lantern, Little Wish is a Lantern Rite Tale in the Liyue region of Genshin Impact. It is part of the first stage of Lantern Rite Tales, and you will need to have complete The Origin of the Lantern quest to access it.
When you accept the quest from the event page, a waypoint will appear near the Dihua Marsh Statue of the Seven. Teleport there and speak with Mengmeng. She will want help learning how to make a Xiao Lantern. This happens automatically, and you do not need to give her one.
After that, head for the new waypoint and speak with Yu. Mengmeng will give him a Lantern, and he will ask for help hanging it on his house. The house is slightly awkwardly designed with an overhanging roof, so climb the pillar shown in the image below.
Climb up to the roof and hang the lantern. This is much easier if you a character like Venti, who can boost himself up onto the roof with his abilities.
The next step will see Yu complaining about needing to clean, so you offer to help him. Equip an Anemo character and use their abilities to blow the dust patches off the ground. Just keep hitting the dust piles with Anemo abilities or charged shots from Venti until they are all gone.
When that is done, go speak with Yu and Mengmeng to finish up the quest. You will get 30 Primogems, 20000 Mora, and 100 Festive Fever.