If you've ever been on Instagram outside of the app, you'll know you're pretty limited in what you can do.
Now - at last - you can add to your story from the web, as long as you're on mobile.
You can also view stories on the web (even on desktop). This feature was apparently rolled out in August but only started working for lots of people today.
This is very handy for people who can't use the app, but sadly posting is still limited - you'll have to make do with still photos and text overlays as video and filters aren't available yet.