Open web.snapchat.com in Chrome or Edge, hover the cursor over the Log In button, and sign in, either by scanning the QR code with your Snapchat app or typing in your username/password (complete 2-FA, as necessary). Always give camera/mic at the request of the browser. Afterwards, you may chat, make video calls, send Snaps and use Bitmoji on your desktop. To note: not all features are mobile.