geez you guys are lazy, if you don't want to explain the right process well don't say anything.
1. Get the frequency of the runway from world/map view (click on the airport, there will be a list of runways with the frequnecies and heading).
2. At about 20 miles from the airport set your frequency in NAV1. Turn the NAv button of the autopilot on.
3. As soon as you will be close enough to ILS range (between 15-25 miles) you will see 2 needles appear on your HSI, one vertically and the other horizontally.
4. There should be a dot or line right in the middle, to the right of your HSI, that's the correct glideslope.
If the needle goes up, you're too low, if it goes down well you're too high. There should be another dot or line in the center (at the bottom) of your HSI this one is for the correct heading.
If it goes to the left, turn to the left, if it goes to the right, turn to the right.
That's how to handle the plane manually in ILS situation, if you want the autopilot to fly it (when there are no strong winds), turn the APP button on instead of the NAV one.
Remember that if you make the autopilot do the approach for you to disegage the autopilot at 300 AGL or the plane will smash on the runway.
Also make sure that you are set to NAV and not GPS.
Looking at the picture below might help you.
Click for large version
Photo © Julian Whitelaw