Using the Instagram App
Instagram is an online mobile photo-sharing, video-sharing and social networking service that enables its users to take pictures and videos, and share them on a variety of social networking platforms, such as Facebook, Twitter, Tumblr and Flickr. - Via Wikipedia
Instagram has now been acquired by Facebook and allows users to instantly share (to various social network services), manipulate and follow photos taken by yourself and other users.
You may download it directly from the web App Store and have it sync to your iPhone.
You can download via the App Store on your iPhone as well.
You will also be presented to login via Facebook to speed things up.
Take pictures with your device and share it instantly with friends. You may also follow other friends and see what they are up to. Manipulate the photo by adding cool effects.