Radio Button
A radio button is a two-states button that can be either checked or unchecked. They are normally used together in a RadioGroup. When several radio buttons live inside a radio group, checking one radio button unchecks all the others.
Example:-
First create a layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout&#95;width="match&#95;parent"
    android:layout&#95;height="wrap&#95;content"
    android:orientation="vertical"
    android:padding="5dp" >

    <RadioGroup
        android:id="@+id/genderRadioGroup"
        android:layout&#95;width="match&#95;parent"
        android:layout&#95;height="wrap&#95;content"
        android:orientation="horizontal" >

        <RadioButton
            android:id="@+id/male"
            android:layout&#95;width="wrap&#95;content"
            android:layout&#95;height="wrap&#95;content"
            android:text="Male" />

        <RadioButton
            android:id="@+id/female"
            android:layout&#95;width="wrap&#95;content"
            android:layout&#95;height="wrap&#95;content"
            android:text="Female" />
    </RadioGroup>

    <Button
        android:id="@+id/knowGender"
        android:layout&#95;width="wrap&#95;content"
        android:layout&#95;height="wrap&#95;content"

        android:layout&#95;margin="5dp"
        android:text="Know Gender" />

</LinearLayout>

Now instantiate UI inside onCreate method of your activity class

// instantiate UI
maleRadioButton = (RadioButton) findViewById(R.id.male);
femaleRadioButton = (RadioButton) findViewById(R.id.female);
submitButton = (Button) findViewById(R.id.knowGender);

Now handle click listener on submitButton

submitButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                if(maleRadioButton.isChecked())
                {
                    Toast.makeText(Test.this, "Selected gender is Male", Toast.LENGTH_SHORT).show();
                }
                else
                {
                    Toast.makeText(Test.this, "Selected gender is Female", Toast.LENGTH_SHORT).show();
                }
            }
        });