You can buy a Habbo room directly from nft.habbo.com on December 14th, or if they're sold out you can buy one on from NFT marketplaces such as OpenSea.
December 14th Habbo X room mint
December's release has both a whitelist which is not over-allocated, and a secondary "reserve" list which is over-allocated. Wallets that are whitelisted will get priority when minting all five sizes of Habbo X room.
We'll be running giveaway for whitelist spots on our Twitter and Discord. Twitter and Discord are also the best places to find upcoming information about how you can secure a whitelist spot.
If you don't get a whitelist spot, it might be that you're able to get a spot on the reserve list. Indeed, wallets that contain at least one Habbo Avatar or one Habbo Portrait will be able to get on the reserve list by default – make sure to keep an eye on our Discord and Twitter for information about how to do this. There will also be a public mint after the whitelist and reserve lists have finished minting.
We'll be publishing final, precise information about the mint schedule and mechanic closer to the time, so keep an eye on our Twitter page and Discord server.
Binance has a good article that explains how whitelist processes work, and the benefits to both sellers and buyers. You can read it here.