The two main places you will access the compression interface are in the edit view and in the multitrack view. To access the interface in the edit view, go the "Effects" menu, choose "Amplitude," and then choose "Dynamics Processing." To access the interface in the multitrack view, click on the "FX" button on one of the tracks, open the "Amplitude" list and double-click "Dynamics Processing." The interface has four tabs. The "Graphics" tab has a graph that represents the amount of compression. The "Traditional" tab allows you to enter in your own values for variables like ratio and threshold. The "Attack/Release" tab lets you adjust the attack and release times for the compressor. The "Band Limiting" tab allows you to adjust which frequencies will be affected by dynamics processing for tasks like de-essing.
The "Graphic" tab allows you to adjust the compression by clicking and dragging the nodes, or white squares, which appear along the blue line of the graph. Check your ratio, threshold and compensation gain by watching the dialog box on the side when in edit view or at the bottom when in multitrack view. In the "Traditional" tab, enter in the values for ratio and threshold. You can also choose to flatten or expand your dynamics processing at different points. Adjust your attack and release times to fit the audio you are processing.
The Adobe Audition 1.5 dynamics processing has several compression presets. While you shouldn't depend completely on the presets to get a good sound, they offer a useful starting point. Choose one of the "VocalComp" presets for vocal compression suitable for voice-overs or broadcast vocals. Try one of the drum compression presets to get more punch out of your drums. Audition offers several limiting options in the dynamics processing section as well. Use the compression or limiting presets that have a soft knee to obtain a more subtle compression. If you find a preset that you like, but it doesn't quite do everything it needs to, experiment with the variables to get just the right amount of compression. If you mess up, choose the preset again to reset the settings. Use the "Preview" button to hear the results of the compression before you apply the compression. This allows you to get a taste of the sound without having to process the entire audio.