How do I view my NFT on the browser extension?
The MetaMask browser extension does not natively support displaying NFTs (source).
How do I view my NFT on the mobile app?
MetaMask's mobile app correctly shows NFTs but you may need to import it manually.
The "Address" is the 42-character hexadecimal (a-z, 0-9) string that starts with 0x...
The "Collectible ID" is the token address of the NFT. For ERC-721 collections, each NFT has a different token ID. For ERC-1155 collections, all NFTs of the same type share the same token ID.
Example:
On PolygonScan: 0x87D549BF461c9Bb6018a7469Ef20FBA2b988c9E5).
On OpenSea:
MetaMask also has an "NFT detection" feature (Security & Privacy > Autodetect NFTs) for Ethereum NFTs only.
See How do I let others view my NFT? for alternatives ways to view your NFT.