To save an entire creation you’ve made in SoundRecorder to disk, click the floppy icon or left-drag from the display window to the Tracker or Desktop. This creates an AIFF file. If you want to save in another file format, Ctrl-drag or right-drag the clip. When you release the mouse button, you’ll be prompted to select an audio file format from among your installed writers (see /boot/beos/system/add-ons/media/writers).
If you want to save only a segment of a track, drag the semi-circular endpieces of the progress indicator left and right to cordon off the selection you want first.

Use the semi-circular draggers to create selections in SoundRecorder.