Layoff notice, what does the 60 days mean? (Louisville)

I received a formal notice about a mass layoff at my workplace. Thank you in advance. I do not know if I should start looking now or wait for severance news. Has anyone been through this?

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

I stayed for the retention bonus and looked for work on the side. It cushioned the gap.