To access Snapchat in a browser, navigate to web.snapchat.com, and sign in with the email address and password.
Once you're logged in, you should see a list of your friends on the left, and a camera icon in the center, that allows you to capture and send snaps to your friends.
You can also click on the Phone icon to start an individual or group call through Snapchat. Similarly, you can message someone.
Snapchat for the web is not available on all browsers—it's currently only available on Chrome or Microsoft Edge.