Bluetooth connection with Android

Hi, I am working on a project, it consists in a bracelet with a button and an app for the phone. The idea is to connect the bracelet with bluetooth, I was searching but all I find is how to switch on/off a Led from the phone. But what I need is when you press the button, the app activates.

The bracelet has to be as little as possible, I was thinking that the button from a selfie stick could be used.

I would do all the investigation to program the Android app and the bluetooth, what would help me is to know what components I will need, so I can design de bracelet, start searching for prices and programming.

I write the post here, because I assume that I will need a microcontroller.

Please, notice that I have little knowledge in this area, but I only need the initial push, and then I go on mi own.

Sorry for the english, I'm from Argentina. Anything that you don't understand, let me know and I explain again.

Thank you.