Click on the play button to check the audio.
Zoom in little on timeline. (optional step).
Right click on audio track click on tools and click on general.
Drag the fade in slider to the right side, as long as you want the fade in effect
to open clip properties there is another way for that click on edit menu click on tools and click on general.
Fade out –
same way you can drag fade out slider to add fade out effect.
Click on the play button to check it.