Connecting SDK(API)

I’ve just starting to learn programmer and I still can’t fully understand the concept of SDK(API).

My aim is to dig into Android SDK so I can utilise the function for my phone (Example: Getting the mobile’s current time)

What is the actual process on accessing the SDK? Do I have to link it with my Visual studio? I had Android setup on my phone but I still don’t have a slight clue on how to get into the Android SDK.