Severance and unemployment, do they overlap?

My employer is paying severance in instalments and I am not sure whether to file now. This is my first time dealing with any of this. I have a mortgage and need to plan. Who should I ask before signing?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.

I filed on day one anyway and reported the severance honestly. The agency decided what to do about the timing.