Layoff notice, what does the 60 days mean? after 15 years as a web developer

My employer announced that the site will close and gave us written notice. Thank you in advance. I do not know if I should start looking now or wait for severance news. Has anyone been through this?

Start your search early. I wish I had begun the day of the notice.

Write down key dates and keep copies of the notice. Mine helped when a question came up later.