Basic Audio Editing

1. The Undo feature

This is one of the most important features to know about. Adobe Audition keeps backup copies of your sound, one for each change you make, and is able to go back to what was previously your file, if you pres Ctrl + Z. Note that these backups are discarded once you close the program.

2. Making a selection

To select a section of a file (in edit mode) you want to work on, you use the mouse as you would for selecting text in a word processor: you click at the position you want to start your selection and drag the mouse, while keeping the left button pressed, to the position you want to end the selection; at that point you release the mouse button.

3. Record 

If you need to record something and you are in multiview mode, you need to decide on a track you will record on. Skip to the next paragraph if you are in edit mode. You most likely want to select an empty track. Once you decided on the track you want, click on it, and arm it for recording. Arming for recording means that you look at the left end of the track and click on the red button with an “R” on it.

You can start recording by then clicking on the record button in the bottom section (where the controls are). To stop the recording, click on the record button in the bottom section again. If you are done recording on that specific track, it is best to disarm it, by clicking the red “R” button again (only in multiview mode).

 If you can record from multiple devices, you can select the one you want to record from by clicking the button below the arming button (you need to be in multiview mode). 

If you want to record from the microphone input, you don’t need to worry about selecting the input device. Just arm the track and press record. It will just work.

4. Deleting part of (the whole content of) a track 

Select the part you want to delete by clicking on it. Then press Del key.

5. Moving a sound along the timeline (within the track, or to a new track)

Click the part you want to move, and drag it to where you want to put it.

6. Splitting a sound 

Select the track with the sound you want to split. Notice a vertical yellow cursor that goes through all tracks. Drag that cursor (by clicking and dragging the top yellow triangle of the cursor) to the point you want the sound to be split. Use the Edit - Split menu item.

General notes:
Red color is generally used for recording. A recorded sound looks red in the track. Green is used for existing sounds.

Example usage: Cut the start / end of an audio file
Start Adobe Audition; you will then have an empty session. Click the first track. Right-click and select Insert-Audio; select the file you want to process. After loading (it may take a few seconds) double click on the sound. This will take you from the multitrack view to the edit view. Select a part you want to remove. Press Del. Repeat this for all parts you want to remove. To save your work, use File - Save As.

Check this link out!
https://www.youtube.com/watch?v=QXJ8aqvv9p4