Web design process simply answered.
What is a Domain name:
A domain name is the registered name of your website.
It is the name that your client would type to find you in google. ie: Tescos.ie or Cocacola.com
You purchase a domain name annually from a local domain registrar.
What is Hosting:
Website Hosting refers to the process of placing your website files on the internet where your clients/users can access your site.
You would buy hosting usually off a third party hosting company or through your web designer.
Some popular hosting companies are: Blacknight, hostgator, godaddy.
What is SEO:
SEO which stands for Search Engine Optimization is the process of improving your ranking on search engines such as Google and Bing. There are various techniques to do this.
SEO is work that has to be done on a continuing basis. It can also be labor intensive.
Having a well designed and optimized site can improve your SEO.