Intent i = new Intent(Intent.ACTION_SEND);
i.setType("text/plain");
i.putExtra(Intent.EXTRA_SUBJECT, "Sharing URL");
i.putExtra(Intent.EXTRA_TEXT, "http://www.url.com");
startActivity(Intent.createChooser(i, "Share URL"));
If the app you want to share to is not installed on the user's device, for example - facebook, then you'll have to use Facebook SDK.
If you want your Activity to handle text data shared from other apps as well, you can add this to your AndroidManifest.xml: