A brief explanation of 301 redirects

If you need to change the URL of a page, we recommend that you use a server-side 301 redirect instead, as shown in search engine results. This is the best way to ensure that users and search engines are directed to the right page. A 301 status code means that a page has been permanently moved to a new location.

301 redirects are especially useful when: You've moved your site to a new domain, and you want to make the transition as smooth as possible. People arrive at your site through several different URLs. For example, if your home page can be reached in multiple ways – for example: http://example.com/home, http://home.example.com, or http://www.example.ae – it is a good idea to choose one of those URLs as your preferred (primary) destination, and use 301 redirects to send traffic from the other URLs to the preferred URL.

You can use Webmaster Tools to set your preferred domain. You are merging two websites and want to make sure that links to old addresses are redirected to the correct pages.

To apply a 301 redirect to websites hosted on servers running Apache, you'll need access to your server's .htaccess file. (If you're not sure about your access or server software, check with your web hosting company.) For more information, see the Apache .htaccess tutorial pages

And the Apache URL Rewriting Guide. If your site is hosted on a server running other software, check with the host for more details.