Think of Intent as a message to allow the application to request action from the other application components (like activity), for instance VIEW, CALL, PLAY etc.

Suppose, on your Facebook app, the running activity is the Newsfeed, and you want to view (in full frame) a pic your friend posted. The click action on the photo would be the View Photo Intent, and the Photo screen (which is a new activity) gets loaded on the click (as the message is communicated).