I don't see the popup bubble.

Make sure you have javascript enabled in your web browser preferences.   Javascript is required for many aspects of the Better Letter application to function.   You can usually find this in the security sections of your preferences.

Sentences of my finished letter do not appear in the bubble after I have finished my letter.

This can often happen if you re-used text and modified it very little, or not at all.   Nobody needs to read the same thing twice, and even if they do, we have a button for that!   To ensure your words appears for others after you, you should modify any recycled sentences to be more unique, or just write something of your own.   One original sentence makes a huge difference!