how to create intent in android code example

Example 1: intent android open activity

Intent intent = new Intent(this, DisplayMessageActivity.class);
        intent.putExtra(key:,value:);
        startActivity(intent);

Example 2: intent android

Intent intent = new Intent(MainActivity.this,Activity.class);

Example 3: intent android

Intent intent = new Intent(MainActivity.this,MainActivity2.class);
 intent.putExtra("key",value);
 startActivity(intent);
////////////////////
 String string =getIntent().getStringExtra("key");