A Live Photo captures a small amount of video before and after the still snap, including the audio, putting your picture into context. All you need to take Live Photos is your iPhone (6s or later) and the Camera app.
To take a Live Photo, in the Camera app, tap the icon showing a series of concentric circles. It’s in the top–right corner, assuming you’re holding your iPhone in Portrait mode (as seen in the screenshot here). With this option active, just take a photo in the usual way, and it’s a Live Photo.