Severance and unemployment, do they overlap?, mechanic here

I was offered severance of 18 weeks after being let go as a mechanic and I am unsure how it affects benefits. I have read a lot of threads here and could not find my exact situation. I have a mortgage and need to plan. Did you file straight away?

Before signing, I asked a friend who is a lawyer to look at the agreement. It was a short conversation and worth it.