Text board and Android keyboard like log-in

Hi, I'm new to Unity3D

I need to open a text box and enter some text using Android keyboard and save the text in a string.

Can some one please help providing example for this in C#?
It is like a user name acceptance field in any website.

My algorithm is this...Can some one help me with C# example ? I tried for a day already

If(Button Clicked)
{
Open text field;
Open Keyboard;
When Keyboard 'Enter'/'Ok' pressed close keyboard;
Save text to a field;
after saving, do something;
}