You can split a song in different parts using the visual editor. When you load a track into the application, a waveform will be displayed. Simply click and drag to mark the selection and then press CTRL + X to cut that part. Go to File > New and use Paste or CTRL + V. It works just like you were managing files on your computer.
To join the files, open each of them, select the section by clicking and draging on the waveform and press CTRL + C, then switch to your main track and click at the end of the track. Press CTRL + V and songs will be joined.