I am using Windows 10 and I want to apply music at the beginning and the end of my Podcast which also an import file as well; how do I do that. Thank you in advance. 
Assuming that you have three audio files: Intro music, Podcast, end music:
(Tip: For best quality, you should use WAV files.)
- Import the three files into Audacity
- Zoom out a bit so that you can see some empty space beyond the end of the podcast (see: https://manual.audacityteam.org/man/zooming.html)
- Use the Time Shift Tool to slide the tracks left / right as necessary so that they play in the correct order.
- Export the finished podcast.
Tip: Export two copies of the podcast. One in MP3 format (your actual finished podcast), and the other in WAV format (your backup copy).
MP3 encoding always reduces the sound quality a bit, so best to use WAV during production and for backups and only use MP3 when you have to.