It's a website! You just literally go to Snort.social and login with your private key. Even better would be to get nostore which is an apple app or browser extension(not an apple user, so I've heard good things but I am no help on that part) to store your private key so you can sign into any Nostr site without needing to paste your nsec. But I've used it countless times without issue. Works great on both mobile and desktop.