How does one use the KEEP WARM feature in a microwave oven?

I can only assume that your oven is a combination microwave/convection oven, as there is now way a standard microwave could ever have a "keep warm" feature...it is just not consistent with the way microwaves cook food. I have a microwave/convection oven with a keep-warm setting. On that setting, microwaves are not used, instead the electric coil inside the oven does the heating. My oven has three different "keep warm" settings based on temperature (low is about 135° F, medium is about 145° F, and high is about 160° F). You set the temperature you want, then place the already-cooked food inside, and the convection oven will keep it at whatever temperature you set the oven at.

I have a Panasonic as well,but mine doesn't have that feature.You must have a manual with it,look in that to see how it works.If you have no manual you can google manuals & choose whichever suits your microwave.