The how to stuff is on here:
http://www.nomorepanic.co.uk/forumdisplay.php?f=60
There are other threads Admin have to explain certain functions. If you get stuck post a thread on that board and they are usually quick to respond.
Clicking QUOTE will insert the correct tags around the person's post and open you up on a new screen where you can type your response below.
MR allows you to QUOTE against multiple posts. To get it to work you click the MR under each one you want to reply to. You then press the QUOTE button on any of those posts and it brings up the same new screen as above just with all the selected posts in. You can then space them out and write in between each quoted post in the same way as you can with any copied text in any word processing software with the Space & Enter keys on your keyboard but make sure you do that at the end of each set of tags.
Don't worry about it, we're used to new people working the functions out. What you've done is fine anyway, you don't have to use the functions and you've been clear by writing the person's username at the head of your post.