Ripple editing is a function in REAPER that allows you to perform editing on a track-by-track basis. You can set it to 'per track' or 'all tracks.'  Although ripple editing can be helpful when you need it, I recommend that you leave it disabled for the most part.  The ripple edit button is located on the top left toolbar in REAPER. Learning to use the ripple edit function in REAPER can aid you in improving your editing workflow.