Thank you for taking the time to post your question.
There are a few dozen audio editing applications that will work with Mac and Windows, and each application has their own learning curve. My top three choices would be Ableton Live, Garageband, and Audacity.
All three programs will allow you to import your songs, select specific parts of each song, and seamlessly combine them together with fades. If ease-of-use is a deciding factor I would place them in the following order:
- Ableton Live
Regarding compatibility, Audacity and Ableton Live are compatible with Mac OS and Windows. Garageband is compatible only with Mac OS.
In terms of cost, Audacity and Garageband are free. Ableton offers a few versions of the application, with the cost matching the features available in each version.
I hope this information is helpful. If you have additional questions let me know. Thank you.
Pedro P. // Audio Engineer