To set an avatar & banner, click the Avatar circle or the Banner square and you can upload an image or select an NFT from your gallery. Your NFT gallery displays all of your NFTs, aggregated across all associated accounts (NFD, Owner, & any linked accounts).
Fill in any metadata you would like to add and then scroll to the bottom and select 'Update metadata' to save these records in your NFD.
Please remember all information is fully public. Do not enter sensitive personal info.