Most important Status Codes that SEOs need to know about them:
301:
Permanent redirection code, will tell search engine that this document has been removed permanetly to another locaiton, search engine will transfer the page rank and ranking (not in all cases) to the new page. Make sure to use 301 redirections when you move your documents to different locations or change your domain.
302:
Temporary redirection code, will tell search engine that this document has been removed temporarly to another locaiton, search engine will not transfer the page rank and ranking to the new page. Many webmasters set 302 redirection by mistake as it is the the default code uless you declare 301 redirecgtion. Make sure that you didnt use it by mistake.
200:
Everything is ok, the document is existed in the same location, thre is not any type of redirection in place
404:
Very important code to tell search engines about removed documents, it is very important to make sure that your server returns 404 code preoberly, you can easly do that using this tool and any fake URL on your website www.yourebsite.com/dd/nonexist/. If your server returns 200 code for no existed documents that may cause you some duplicate content issue with search engines