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There are lots of ways to do this. You could solo a track and choose File > Bounce...
Or, choose Track > Bounce All in place
(the resulting audio regions will all be in the Bounces/audio files folder of the project.)
If you're taking your stems to PT or another DAW to mix, then you should always make sure to bounce / export all tracks at the same start point.
The File > Export > Export all tracks
command can be useful if you don't want to render all non-volume and pan automation to each audio file.
Hope this helps