What is a 301 redirect and when do you use one?

A 301 redirect says permanently that an address has changed. That word "permanently" is what sets it apart.

What it does

Visitors land in the right place and search engines transfer the value of the old page to the new one. Without it you start from zero on the new address.

When you need one

When changing URLs, merging two pages, moving to https, or choosing between the www and non-www version. That last one is most often forgotten.

The 302

Temporary. Only use it if the old address genuinely returns. A 302 left in place for months prevents value from transferring.

Avoid chains

A redirect to a redirect to a redirect is slow and loses value. Point straight at the final destination.

Do not redirect everything to the home page

That is the classic mistake during a rebuild. A visitor looking for a specific page who lands on the home page leaves. Redirect to the equivalent page, or to nothing.