A redirection 301 by means of haccess is necessary when we have a page that we have recently updated, for example the site was done in flat html (or it can be xthml, flash or whatever) and now the site we migrate it to a content manager (the one you want). So at the entrance all the URLs are going to change, where they were called www.midominio.com/ us.html Now it is called www.midominio.com/nos To change it the best option if you are on a Linux server (90% of the Servers with web output) The ideal is to modify the .htaccess file (see that the file is not hidden and can be edited).
Then just add a few lines and ready
redirect 301 /url_antigua.html http://www.midominio.com/url-nueva/
Eye It is important to put only /url_antigua.html and not the complete domain, then in the second part for example at http://www.midominio.com/url-nueva/ there you can even change the domain if your website is called another way.
Do you want to know more about the redirects that are not penalized by Google? To know more about redirects 301 and other things you can consult in http://www.master or watch the following video