Before we begin, you may be asking yourself, what is a redirect? A redirect is basically just an instruction that is sent to your browser to tell it to go somewhere else.
Why would you want to use a redirect? Ideally, you would avoid using redirects altogether because you would never change the URLs to your web pages once they're published. It's been said many times, many ways, good URLs don't change.
The ideal goal is to have a permanent URL, but no matter how hard you try to stick to this philosophy, you will inevitably end up in a situation where you need to move a document, especially if you're new to web development and site design. When moving a document, the important thing to remember is that this change carries many implications reaching far beyond updating all of the links on your own website.
There are many members of your audience that will be affected when you move a document. If you simply move a document to a new URL, sites that link to the old URL will have broken links on their site, people's bookmarks will no longer work and search engines will discard all information on the old URL and will have to start a new record for the new URL from scratch.
How do we avoid all of this? We have to use a redirect to notify people about the new URL and transport them to that new URL.