Explain Android Development

Hi im in college and i am starting to make an android game. Can you help me by explaining where i should start and i’ve seen some forums and people are talking about an android SDK. Can you explain me what it is and if i can start creating the game in unity or if i need to go to SDK

Not sure how you failed to find this when searching for information:

http://docs.unity3d.com/Manual/android-GettingStarted.html