Placing rectangle in Android

Before commenting on how to do what you ask, it is important to review the drawRect() method of the Canvas class , which has several implementations, you can see that it can receive the left, top, right, and bottom points as well as the Paint object:

void drawRect (float left, 
                float top, 
                float right, 
                float bottom, 
                Paint paint)

The points indicate the position in which the rectangle (or square) will be drawn, in the case of android the coordinates 0,0 start in the upper left position:

similar to the fourth quadrant of a Cartesian plane:

You can create a class that creates your rectangle, in this case it will start drawing it at coordinate 0,0 and as an example 400 pixels wide by 200 high:

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;

public class Rectangle extends View {
    Paint paint = new Paint();

    public Rectangle(Context context) {
        super(context);            
    }

    @Override
    public void onDraw(Canvas canvas) {
        paint.setColor(Color.GREEN);
        paint.setStrokeWidth(3);
        canvas.drawRect(0, 0, 400, 200, paint);
    }

}

and display it in your Activity:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Rectangle rectangle = new Rectangle(getApplicationContext());
    setContentView(rectangle);


}

Resulting:

On the other hand, if we want it to be displayed at the bottom, we can increase the value of topy bottomso that it is positioned vertically downwards.

I have seen that what you want is to make a game, so I will give you an example of how to move the rectangle, by drag and dropusing the previous class to create the rectangle:

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/root"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Move the rectangle!" />
</RelativeLayout>

Using OnTouchListener, touching the view and dragging it will move it to the desired position, modifying its position.

MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {

    private RelativeLayout rootLayout;
    private int _xDelta;
    private int _yDelta;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //activity_main, debe contenerse dentro del layout activity_main.xml
        rootLayout = (RelativeLayout)findViewById(R.id.root);
        Rectangle rectangle = new Rectangle(getApplicationContext());
        rootLayout.addView(rectangle);

        RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(200, 200);
        rectangle.setLayoutParams(layoutParams);
        rectangle.setOnTouchListener(this);

    }

    public boolean onTouch(View view, MotionEvent event) {
        final int X = (int) event.getRawX();
        final int Y = (int) event.getRawY();
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_UP:
                break;
            case MotionEvent.ACTION_DOWN:
                RelativeLayout.LayoutParams lParams = (RelativeLayout.LayoutParams) view.getLayoutParams();
                _xDelta = X - lParams.leftMargin;
                _yDelta = Y - lParams.topMargin;
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                break;
            case MotionEvent.ACTION_POINTER_UP:
                break;
            case MotionEvent.ACTION_MOVE:
                RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) view.getLayoutParams();
                layoutParams.leftMargin = X - _xDelta;
                layoutParams.topMargin = Y - _yDelta;
                layoutParams.rightMargin = -250;
                layoutParams.bottomMargin = -250;
                view.setLayoutParams(layoutParams);
                break;
        }
        rootLayout.invalidate();
        return true;
    }

}