Cranberry Sauce and Cranberry Jelly are the same thing but just come in different forms.
The main difference between the cranberry sauce and cranberry jelly is in the pectin that it contains.
The cranberry jelly is solid enough to retain the shape of the container in which it's placed whereas the cranberry sauce version is much more fluid.
Some people warm up canned cranberry sauce and some people just serve the canned cranberry sauce cold or at room temperature right out of the can.
You can serve the canned cranberry sauce either way.
My mom would warm up canned cranberry sauce before she served it and my Grandma always served the canned cranberry sauce cold.
It's all up to you and is a personal preference.
If you prefer the canned cranberry sauce warm then warm it up but if not you can serve it cold or at room temperature.
Cranberry sauce is usually served cold or chilled.
But if you want to heat the cranberry sauce up you can do so.
I like my cranberry sauce heated up so that it's warm but not too hot as it tastes better than being chilled or served cold.
However I do sometimes like to make cranberry sauce sandwiches by placing cold cranberry sauce out of the can onto some bread and eat it that way.
But when you eat cranberry sauce for Christmas or Thanksgiving dinner it's traditionally served cold or chilled but it's okay to eat it warmed up if that's the way you prefer it.