Android users rejoice: The long-time iOS photo-sharing app Instagram, which has been one of the most popular social start-ups despite only being housed on a single platform, has been released on Google's mobile operating system. The app is currently available as a free download from Google Play (nee the Android Market).

Kevin Systrom, who co-founded Instagram back in October 2010, announced at SXSW in March that Android users would finally receive his popular app in the cmong months. The company released a sign-up page for users to be notified when it went live, and now it has.

For those who are new to Instagram, here is a guide of the best features on the ultimate photo-taking and sharing platform.

The Feed: Identical to its iPhone counterpart, Instagram's news feed on Android shows recent uploads from friends and users on Instagram that you choose to follow. Like the familiar News Feed on Facebook, users can like others' photos or comments, or scroll endlessly.

Filters: By far the best feature of Instagram is its ability to give your photos a look and feel that your camera couldn't create alone. With 18 different filters, which can bring out the warm tones in a picture or make it into a stark B&W old-timey photo, playing with filters on different photos is part of the fun of owning Instagram. Just take a picture or select one from  your Camera Roll, and test out some accents.

Popular: Besides stylizing your photos and looking at your friends' photos, you'll want to see some of the best across the entire Instagram ecosystem. The popular tab (characterized by the Star tab, second button to the left at the bottom) can give you a good picture of what's popular and trending across Instagram's 10 million-plus users.

News: The home page is great to look at others' photos, but Instagram has a separate page for users to check out others' recent comments and likes, called News (second button to the right on the bottom). This is useful to look at because you and your friends don't all follow the same people, and checking out the News tab can give you an idea of who to follow on the massive platform.

Profile: Once you've put a bunch of your old photos through Instagram's beautiful filters, you'll want to see them all in one place. On your Profile (the tab furthest to the right at the bottom), you can see who you're following, who's following you, and the number of uploaded photos you've provided. Furthermore, you can see all of your photos in a simple way, either in a grid or a list.

In September, shortly after launching version 2.0 for iOS users, Instagram announced that the service had experienced a sign-up rate of roughly one user per second, or about 78 users per minute. The company's peak upload record was set on Sept. 26, when Instagram users uploaded 26 photos every second.

Since launching in October 2010, soon after the release of the iPhone 4, Instagram has amassed more than 10 million users, and has attracted celebrities like Snoop Dogg and Justin Bieber; comparatively, FacebookTwitter, and Foursquare, all hot start-ups at one point, each took over two years to reach the same 10 million user mark. 

The first iteration of Instagram allowed users to take pictures, add smart effects and filters, and upload the photos through Flickr, Tumblr, and Facebook. At this point, no one had achieved this level of interconnectivity with other platforms.

Many services like to keep content to themselves, but we like to push it out to other services, Systrom said. That was a real pain point for people, and that's one of the things that made us stand out from the beginning, I think.

The speed at which Instagram's app runs also gave Instagram a competitive advantage.

When you're with a friend at a café or whatever, you don't want to waste five minutes waiting for your phone to upload a high-resolution image, Systrom said.

Instagram 2.0 runs even speedier than its first version because of its technology that uploads the photo before it's even finished being edited. In addition, Instagram made filters applicable to photos before they're even taken, which allows the company to accommodate higher-resolution photos and maintain its same speed.

Instagram 2.0 also features larger images for print and framing purposes, and the ability to rotate images, add or remove borders and tilt shift, or blurring a section of the photo. Instagram on Android, however, does not feature tilt shift. Yet.

In a space where a lot of people are trying to attack the same problem, we think our goal should be to really lock up the space, Systrom said.

Instagram for Android works with Android version 2.2 or higher.