Hi, I am very new to Vegas Pro and would like to have 2 of my audio files playing simultaneously. How ever if I put them on top of each other only one of them plays, I'd like to hear both of them at the same time. Thanks in advance.
Put them on separate audio tracks.
Each audio file needs to be on a separate audio track. Right click the track header window (far left of the timeline) or the timeline itself and select 'Insert Audio Track'. Your will now have 2 audio tracks. One audio event goes on one track and the other audio event on the second audio track. You can use the volume control in each track header to adjust the volume of each track.
You may find useful some Vegas Pro tutorials covering the basics of editing in Vegas Pro. There are five of them from a year ago, the first being 
There lots of other tutorials on Vegas Pro's webpage as well: https://www.vegascreativesoftware.com/us/vegas-pro/online-tutorials/
Check to see that one of the tracks is muted or solo'd. Either could cause only one of the tracks to be heard (assuming of course the files are on separate tracks).
The mute and solo buttons are in the track(s) header.. if they are not visible, click the hamburger icon (track header, upper-left) and choose "Edit visible button set"