Flash MX 2004 Actionscript HELP!

I am new to the flash/actionscript world and I am trying to create a very simple space invaders type game, (a vertical shooter).

I have been using a number of tutorials to help me in different areas and I have so far got my space ship to move left and right and an alien to fall from the sky. However, I am having real trouble with firing a bullet from the spaceship (i have made a bullet animation) and making the game end if an alien reaches the bottom of the screen. Some code that I tried from tutorials in order to do this either simply did not work or posted errors which I couldnt understand!

And I can also anticipate having problems making the alien disappear when shot and keeping score!

If anyone has any code or a knows any tutorial that will work for me I would be very grateful! Any guidance would be very helpful! Thank You