Severance and unemployment, do they overlap? - any advice?

I was offered severance of 18 weeks after being let go as a welding apprentice and I am unsure how it affects benefits. I have read a lot of threads here and could not find my exact situation. The agreement mentions a release and a payment schedule. Who should I ask before signing?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.