To start an activity, you need to use intents. And you can call this when a button is clicked like so:
Button myButton = (Button) findViewById(R.id.MY_BUTTON);
myButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(CurrentActivity.class, NextActivity.class);
startActivity(intent);
}
You can read more about starting activities here.