Use FSCharts.com to find the chart for the airport you are landing at. You'll see all of the runways numbered on the chart, along with ILS frequences etc. For whichever runway you are landing on, tune the NAV1 radio to the frequency shown on the chart and make sure that you are slowed down - 140 knots for a 737 is a good speed. When you are about 10 miles out, hit the "APP" button and let the aircraft do the rest for you. Play around with it and you'll soon get to grips. For a more detailed explanation, have a search of the internet. There is plenty of information out there.