There are basically 4 different addresses that all point to your website. You have an http and an https, as well as a www. and a non-www. version. You should be using https for security and SEO reasons (you can read more about how to setup SSL for free here), and then you will have to pick if you prefer the www. or non-www. version as your main address. I use "https://www." for all my sites, which means that the other 3 addresses should all point to that one. This is accomplished via IIS (Internet Information Services) bindings.
IIS bindings are used to bind a URL address to a website folder that exists on the machine. This is how the machine knows what files to serve to the user when they visit your URL.
Below you will see IIS Site Bindings that enure all traffic to "https://www.redyoshi.com" is served the correct files for the Red Yoshi site.
The "Basic Settings" dialog box controls the location of those files.
Now we need to setup another IIS binding for the other 3 addresses and have it redirect to our https version.Example:
Right click on Sites in IIS and click Add Website...
I will call this one "RedYoshiHttp301", and instead of pointing to the actual files, I will point to any other location. This location will be used to store the configuration.
(I like to create an 301 folder in the website for this.)
Now that RedYoshiHttp301 exists we will setup 301 Redirects for it, in order to redirect to the https version.
Click on the "HTTP Redirect" feature in IIS and setup a 301 like this:
Now click on the "URL Rewrite" for this new site and add 3 rules to improve SEO.
The 3 rules keep everything consistent https address, lowercase, and without the trailing / in the URL.