To make the ILS landing you desire you need to do the following:
Tune NAV1 radio to the ILS frequency (available from the map).
Enter the runway heading (available from the map) into your autopilot COURSE. How you do this varies with the aircraft.
The autopilot may or may not be on. Ensure that it is on and click the APR (Approach Hold) button. The NAV/GPS selector should be on the NAV position. This tells the aircraft to follow the COURSE to the ILS frequency that you have already plugged into NAV1. When you intercept the the ILS radial your aircraft will turn to follow it.
Make sure you are BELOW the glideslope indicator. When you are close enough to the ILS beacon you will see the ILS indicator become active. The ILS indicator should be above you. You will fly straight and level until you intercept the vertical ILS beacon (you will see this in your instruments). At that point your aircraft will appear to make a nosedive but it is really just following the ILS beacon down.
The ILS will NOT adjust your speed. You need to do this by yourself.
Most airports are pretty good at getting you close to the center line but the ILS is not an automatic landing system. With experience you will learn to turn off the autopilot altogether (I do it a couple of miles out for jets, a little closer for props) and finish the landing manually.
Don't get frustrated. You are not going to learn instrument navigation in 5 minutes and it takes practice. Check out some of the tutes here
http://www.simviation.com/fsdhelp.htm and here
http://www.emeraldair.net/training.html
