I'll try to help. You need to do several things.
First go into phone by pressing the green phone key. Click wheel "options" then "general options". Choose NO for "Dial from home screen". You will now have to hit green button to dial numbersh or use speed dial with letters.
Now you have shortcuts available from the homescreen with various letter keys such as L for calendar, U for calculator, K for keyboard lock, and M for messages. However, message may be a text mssg (SMS) or an email, seeming to depend on what you did last (but there is a work around). Now you can hit M (briefly) and you will go right to messages. Or if you have a speed dial assigned to M, no problem, just press it a little longer to dial. Neat!
Now that you are in messages, you can hit C for compose, but this may compose a text mssg or an email depending on what you did last. To avoid this problem use click wheel to select email or SMS (instead of C).
If you really want to, you can assign either of the convenience keys (the middle key between phone keys or the one on the left side) to go right to messages or other function too (you will get a list to choose from). To do this, press O (for options), select Screen/Keyboard, scroll down to the bottom and you can assign functions to these keys. Using an assigned convenience key is a little more powerful for your purpose of composing a message in that when you hit the convenience key you go right to messages without having to be on the homescreen first (as above shortcut letter keys work).
This may sound overwhelming, but once you learn the shortcut keys, they are easy and helpfull.