In one sentence, describe what the following article is about:

Snapchat should open directly to the camera interface. This will take you to the Stories page, where all of your contacts' stories are arranged in order from newest to oldest. You should see a "Chat" option toward the bottom of the screen. Tapping the "Chat" button will freeze the story in place, so don't worry about running out of time. This will overlay the story image with your text. This chat will show up on the "Chat" page as a blue arrow; when your recipient opens it, the blue arrow will become hollow.

Summary:
Tap the Snapchat app to open Snapchat. Swipe left. Tap a story to open it. Tap the "Chat" arrow at the bottom of the screen. Type a message in the "Send a chat" field. Tap "Send" when you're done.