SSL certificates are purchased by your company. There are several companies that can provide them. The first point of contact is probably the company where your domain is registered. Major providers of SSL certificates include:
There are other providers as well that can be found via a web search.
Note that there is a cost for an SSL certificate and it must be renewed yearly.
The following information is copied from the following URL at GoDaddy.com. The URL is correct as of February 1, 2017.
https://www.godaddy.com/help/install-ssl-certificates-16623
To Install an SSL Certificate in Microsoft IIS 7
For Wildcard SSL certificates make sure your Friendly Name to matches your Common Name (i.e. *.coolexample.com).
Visit your website at https://www.coolexample.com (replacing coolexample.com with your domain name) to verify the installation. If you have problems, see Test your SSL's configuration to help diagnose issues.
As a courtesy, we provide information about how to use certain third-party products, but we do not endorse or directly support third-party products and we are not responsible for the functions or reliability of such products.
The use of a certificate issued by a proper authority is highly recommended. Self-sign certificates will cause an unsecured connection warning by browsers.
The following shows how to create a self-signed SSL certificate.