Open the list panel with the “List” button at the top right corner (or open a List window with Ctrl+L). Resize the panel so you reveal the file list. From this you can browse for your wave files and then drag them onto the tracks.
When you split or resize the sound events on the tracks, this is done non-destructively. If your sound is used multiple places, you can use the “clone phantom sequence” command to make a unique instance. When it’s unique, you can use the “crop unique sequence” command to trim the sound to the contents shown in the event. When you select the event, you can do destructive waveform editing using the sound editor.
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