Abrir Menu Android

Android.java

 @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.menu, menu);
        return true;
    }


 @Override
    public boolean onOptionsItemSelected(MenuItem item) {
 
        switch(item.getItemId()){
            case R.id.menuAbout:
                Toast.makeText(this, "You clicked about", Toast.LENGTH_SHORT).show();
                break;
 
            case R.id.menuSettings:
                Toast.makeText(this, "You clicked settings", Toast.LENGTH_SHORT).show();
                break;
 
            case R.id.menuLogout:
                Toast.makeText(this, "You clicked logout", Toast.LENGTH_SHORT).show();
                break;
 
        }
        return true;
    }

https://www.simplifiedcoding.net/android-toolbar-example/#Creating-Toolbar-Layout