Each interview clip or reporter link in your piece should be the same volume.
To ‘normalize’ your clips (make them all the same volume), click on each clip to highlight, press F2 (or go to View, then Media Item Properties), click on Normalize, then click on OK.
Do this for every clip in your session.
N.B. Normalizing boosts or reduces volume for the whole clip, including background noise. So make sure you check levels when you’re out recording.
Render your Reaper project
Once you’ve finished editing your radio piece you need to render it into a single .wav file that you can then use in a bulletin or submit for assessment.
This film shows you how to do that.