Instagram is currently the third largest social network online. Facebook purchased it for a cool 3 billion dollars making it one of their most successful purchases ever.
One of the greatest appealing qualities to the network is the ability to share photos. When sharing photos you can tag photos using hashtags to help categories the images. While creating new posts users can like them giving you a sense of popularity.
If people like your photos they have the option to follow you. When a user follows you they will see your posts in their news feed. The news feed is made up of all of the types of photo you and your friends like.
A quick way to gain likes is to use 3rd party applications on iTunes like http://www.instaliker.us . This is an Apple application on iTunes that works like the most popular Like For Like systems.
These L4L or Like4Like networks allow users to like your photos to earn coins. The user can spend the coins to promote their own posts. Gaining popularity on Instagram is massively in demand. Take a look at the link above to get more exposure on IG.