He hops down onto the floor to give himself a better space to work in. With his wand, Harry begins the work, enlarging the box a bit to start with. He learned how to use curse boxes as an auror, but he didn’t learn how to make them until after he left the Ministry. Most curses can eat through wards if they are inside the warded area, because wards are generally designed to keep things out. A curse box, however, has the wards pointed in the other direction, meaning the curse has to fight the "shield’ side of the ward, while outside influences can still move through the wards and affect the box itself. Generally, a cursed item would be placed in a curse box, which would then be placed in a traditionally warded and sealed container until such a time that the item can be studied and the curse broken. For this particular item, the secondary container won’t be necessary, but Harry isn’t sure what kinds of curses Riddle may have placed on the ring so it will go in the box to start with, until he gets a hold of something that can destroy the horcrux. Fiendfyre is the easiest option but unfortunately, casting and controlling fiendfyre takes more raw magical energy than a five-year-old generally has access to. Honestly, after the incident in the Room of Requirement all that time ago, Harry’s not sure he ever wants to risk trying his hand at fiendfyre.