If you are looking for a digital audio workstation, audacity is a great place to start. Audacity is usually used to record audio or edit audio for things like podcasts. When using audacity, some features you have is the ability to adjust audio levels.
You do this by going to effects and clicking amplify. Finally, you can fade audio in and out with regards to intros and outros for a podcast. When you are recording audio, you will need to get rid of |background noise| so it not distracting to listeners. The easiest way to do this in Audacity is to click on effect and then noise reduction. Audacity also allows you fade in and out an intro or an outro which is very popular when it comes to things like podcasting. 'Importing a file will automatically create a new track..