As the business press covers Facebook's $1 billion purchase of Instagram, and tech sites discuss the app's recent launch on the Android mobile platform, we thought we could answer some basic questions you may have about this very popular app.

1. What exactly is Instagram?
It's a free app that was first available for Apple's iOS devices and is now also available for Android devices. With Instagram, you can take photos, crop them, add borders, pump up brightness and contrast, and choose from a wide variety of fun and artsy effects to enhance your shots (the effects can also help you disguise defects!). You're then able to share your photos instantly with your Instagram followers.

2. Can I share Instagram photos on other social media?
Yes: From within the app, you can choose to share your photos on Facebook, Twitter, Foursquare, and Tumblr. On iPhones, you can also share your shots on Flickr and Posterous and via e-mail (these additional sharing options will hopefully come to the Android version, as well).

3. Can I import existing photos on my phone or online into Instagram?
You can"Instagram-ize" any shot from your existing photo gallery by tapping the camera icon, then selecting the image icon. You can also import photos into Instagram from your phone's memory card or from shared folders via Wi-Fi.

4. Why use this when I'm already sharing photos via Facebook and Twitter?
If you're not interested in Instagram's own sharing network and the fun effects it offers, you may not want the app. But since Facebook acquired Instagram, we'd predict that much closer integration of the app into Facebook is coming; its features may become part of Facebook's own photo capabilities. There's a question as to whether the app will continue as a standalone at all, given the fate of other apps Facebook has bought, such as Gowalla and Snaptu.

5. Was Instagram really worth $1 billion?
Presumably, since that's what Facebook paid for it! But we leave market valuation to the business press. Our take is that Instagram certainly ups the fun factor for mobile photographers and is a breeze to learn and use. Even better, consumers don't have to pay $1 billion, or anything at all: Instagram is free in both the iOS and Android app markets.