Permanent and temporary redirects
301 and 308 are permanent: search engines move the old URL's signals to the new one. 302 and 307 are temporary: the old URL is expected to come back. Use a permanent redirect when a page has moved for good.
308 and 307 keep the request method (a form POST stays a POST); 301 and 302 may turn it into a GET. For ordinary page moves, 301 and 308 behave the same in search.
Why chains matter
Every extra hop costs a round trip, and crawlers stop following after a handful. A common chain is http to https to www to the final page; point all of them straight to the final URL instead.
Questions
Does a 301 redirect lose SEO value?
Google says permanent redirects pass ranking signals to the new URL. Long chains and redirects to unrelated pages are what cause problems.
What is a redirect loop?
A URL that redirects back to itself, directly or through other hops. Browsers give up and show an error.
Should http redirect to https?
Yes, with a permanent redirect, and the www and non-www versions should also land on one canonical host.
How many hops does the checker follow?
Up to 10, then it stops and reports the chain as too long.