This forum remembers what you had posted previously, just in case what you describe happens to you, and 99% of the time you will have your complete post sitting there when you go back to the editor.
If this happens to you again, do not click the back button or anything like that. Just go back to the topic where you were creating your post..... scroll down to the bottom of the page, click on the 'Reply to this Content' and the editor will open up, and your post should still be there. You will get a prompt to clear the editor, do not do this or you will lose your post and it will not be recoverable.
As to regards to you copying your post to another editor. You don't to use any special buttons to copy text, each OS has their own method (key combo's) of copying/pasting text to/fro the clip board. for example, in Windows, just click within the editor, press control-a, control-c, and then use control-v in another editor to past your content.
You do not need to use BBCode with this software (Most of the BBCode code was removed in Version 4 anyway). Just copy and paste from your external editor to the forum editor, you will be promoted to keep the formatting or not.
If you want to bold a word, select the word and click on the B icon at the top of the editor. Just treat this editor like you would most modern text editors - for example Microsoft Word.