The Welcome worksheet is the starting point of the Sheet. It is used by registered users to enter their Personal Key which will unlock all the features of the Sheet. Note that:
Your Personal Key is unique
Your Personal Key must be entered EXACTLY as received (Copy & Paste is the way to go)
Your Personal Key contains an encrypted version of your name. It must not be shared with anyone.
Your Key should be kept in a Safe & Private place.
If your Key is leaked [by any means] to the public, it will be invalidated. You will also loose your access rights to the Forum.
The procedure to enter your Key is simple:
Copy your Key in the Clipboard (select it in the e-mail [without trailing spaces], and press Ctrl-C)
In the Welcome Worksheet, click on the "Enter Registration Key" button
In the window that appears, paste your Key inside (see image below) and press "OK"

If everything is right, then the Sheet will report the successful entry of your Key and some text will disappear from the Welcome worksheet. If you wish to remove your Key from the Sheet, use the "Clear Registration Key" button.