Someone recently asked “what does 5k base mean”.
That probably means your base period of training. This is a period of longer slower runs, typically done over the off-season (winter). This feels like a waste of time as you are not doing particularly strenuous runs.
However amongst other things this sort of base training might improve your technique and will certainly improve how your body burns fat and also improves the point at which your body starts to rapidly fatigue (amongst other things).
This period is seen as putting “miles in the tank”. As you race approaches say 1-3 months away you can start to spend those miles with much faster periods of training. You will be able to better do this training because of what you put in in your base period.
But to be honest you will probably improve doing any kind of running. If you want to look for more look at training plans on this site for 5k or read about “periodicity” in athletic training.