Hi...erm....guest......lol
I had exactly the same problem as you did when i first bought the product too - unfortunately, the manual isnt anywhere near as good as the product itself......
Ok - first things first.......
1) On the MCP, dial in the initial altitude that ATC assign to you on the ground.
2) On the heading selector, dial in the heading of the runway that you are taking off from - ie if you are told to take off from Runway 09, dial in 90.
3) Where i think you may be going wrong is with the speed. Before taking off, you need to arm the Autothrottle and dial in your airspeed - the manual says set this to your cruising speed of 250kts - this is way, way, way over the top - the recommended setting is V2 + 10 - i would say set your speed to no more than 170.
The problem with having a higher speed setting is that when you engage the autopilot by clicking the CMD A button, the jet will attempt to attain the speed by diving the nose, hence more airspeed - an unfortunate side effect is crashing nose first into the ground!
One last thing to point out is to make sure that the Autopilot Disengage bar is set to disengage, ie, up, not down....
Ok - so, now that all your setting have been set, taxi to the runway and take off - at V1, rotate and try to hold your nose at about 12.5 degrees - when your altitude passe 1000 ft, engage the AP by clicking the CMD A button - hopefully, you wont take a nose dive!!!!! If you do, try repeating the same but with a slightly slower MCP speed set for the autopilot.
All being well, the AP will climb to your assigned altitude, and once you are safe that you arent gonna crash and burn, you can increase the speed control on the MCP to 250kts.
Hope this helps fella - if not, repost and i will talk you through some other things you could try......
Good luck, and persevere - it is sooo worth it!!!
Chris aka chrisb440