Each NFT created on Infinifty features a unique storage asset area to upload an unlimited amount of files that you can pass along with the NFT to it's next owner.
From the item preview screen scroll down to the status area to find Storage and tap the Storage button.
Drag files into the Upload area, or browse your device using the browse button. The files you upload are fully decentralised and can be reached from any web browser you can connect your wallet to, including web browsers that load within your wallet, such as with the Metamask app.
As you start adding files you'll see them listed below in the file area.
You can create folders within your Storage area to better categorise the files you upload. You or your NFTs new owner may find this useful, but it's a completely optional step.
Simply add a name for your folder and tap the plus button. Add as many folders as you like.
To assign one of your uploaded files to one of the folders, tap the file in the file area, and assign it from this point.