On calling, an application chooser dialog will appear and by selecting an application you can share your content with it.

For calling use this line of code in your program class:

share(context, "This is a test message", "Test Subject")

Function's definition:

public static void share (Context context, String text, String subject, String title, String dialogHeaderText) {
    Intent intent = new Intent(android.content.Intent.ACTION_SEND);
    intent.setType("text/plain");
    intent.putExtra(android.content.Intent.EXTRA_SUBJECT, subject);
    intent.putExtra(android.content.Intent.EXTRA_TEXT, text);
    intent.putExtra(Intent.EXTRA_TITLE, title);
    context.startActivity(Intent.createChooser(intent, dialogHeaderText));
}

See original post here: http://stackoverflow.com/a/35159850/3819836

This example explain how to use an Intent for start a new Activity.

You need two activities:

1. CurrentActivity
2. DestinationActivity

In CurrentActivity you have to created an Intent. For that you have to specify two arguments:

1. Context: It's CurrentActivity, because Activity is a subclass of Context.
2. DestinationActivity class

Intent intent = new Intent(Context, DestinationActivity.class);

Then, call startActivity passing the intent created.

startActivity(intent);

Now we have this source:

Intent intent = new Intent(this, DestinationActivity.class);
startActivity(intent);

For example, you can put it in a method an call it when an event ocurred.

void nextActivity(){
     Intent intent = new Intent(this, DestinationActivity.class);
     startActivity(intent);
}

public class CurrentActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.current_activity);
        
        nextActivity();
        finish(); // Finish current activity, if you don't finished it, the current activity will be in background. You can finish it then.
    }
}