How to use jarred roux?

I have some jarred roux I bought to take to a friend in Las Vegas but forgot I was flying and did not want to donate to TSA so I kept it. Ready to make some chicken/andouille gumob with the roux but have never used jarred before (always do the nonfat in the oven). Should I heat up my stock and then add the roux spoonful at a time to the stock? Ok to saute the veggies in a little roux or do them separately in a little oil? Advice appreciated.