Summarize this article:

Taking a screenshot of a Snapchat is the same as taking a screenshot of any other app, but you'll need to be able to do it quickly. Taking a screenshot will send a notification to the other person, so make sure you're OK with them knowing you're taking the screenshot. The method for taking screenshots varies depending on your phone:   iPhone - Press and hold the Power and Home buttons.  Android - Not every phone can take screenshots, but most newer ones can. Below are instructions for a few of the most popular Android models.  Samsung Galaxy S Series - Press and hold the Power and Home buttons. Nexus Series, HTC One - Press and hold the Power and Volume Down buttons. Remember, the other person will be notified that you are taking a screenshot. Press and hold the Snapchat to open it. You will see a timer in the upper-right corner denoting how long it will last. Keep pressing your finger on the Snapchat to keep it active. If you have to, do this with your other hand while you continue holding the Snapchat with your finger. As soon as the screenshot is captured, the other user will be notified. The screenshot will be saved to your phone's gallery.

Summary:
Learn how to take screenshots of your phone. Open the Snapchat that you want to capture. Press your screenshot buttons.