You need a domain name and you must register it. That could cost you anywhere from $6.99 upwards depending on your registrar. Research all of them. Domain name with your site theme concept is recommended but not necessary. Most easy website builder package should include this for free.
What is a domain? If you register for domain name, you are the domain owner. There is no legal ownership of the domain name, but just a right of use.
Domain names also help as identification labels to indicate ownership and control of a site. Each domain name has its own identity. Your names and addresses mean nothing online. Unless you have a domain name, the rest of the online world will not know you. Domain name represents your business.
Domain names have a typical address, where the www mean world wide web, and the first set of characters mean a unique name you alone have on the net and the extension kind of represents a particular branch of the internet , etc.
You are charged on an annual fee basis. You never really own the domain but kind of rent or lease for the duration of the time you have paid the fee. If it is very successful and useful, you register for a period like two or five years. You need to renew it every time it expires and if you do not you lose it.
Most packages that offer an easy website builder will include domain registration as a package deal. Therefore, you should not have to worry about the process of searching for and registering a domain for your site.
There is a theory going around that domain names are important for page ranking in the search engines. That is, your keywords should be a part of the domain name. Domain name itself can represent your keyword. This popular notion has not real basis. Google may have increased ranking for random sites and it could be a coincidence.
There is no real proof that this increases your ranking. On the other hand, there is no harm in making your keyword as a domain name. You may have to improvise it with dashes and creativity by adding a word before or after.
It could help in publicity when you hand over your website address to people offline. Nevertheless, there is no inherent importance to domain name and keyword. An easy website builder will help you decide this and register for you.