Instagram launched Stories back in August as basically a carbon copy of Snapchat's similar functionality. Since then, you've been able to see Stories from the people you follow in the top area of your Home tab.
But what if you want to discover other people's Stories too? Well, there's a solution for that now as well. Starting today, Stories will be featured in Instagram's Explore tab too, alongside pictures and videos that aren't part of a Story (and which have been in there from the beginning). This means that Instagram's algorithms will not only suggest people for you to follow based on your interests, but also Stories.
Apparently more than 100 million people visit the Explore tab each and every day, so presumably more eyeballs will check out your Stories from this point on. Your audience when using this feature is no longer limited to those who follow you.