A relatively straightforward way to build a basic website is to use a free package that will provide you with a template web design and a web content management system (CMS).
The following are examples of these free services that provide both a design and a CMS as part of their package:
Alternatively, you can use a standalone CMS. This would mean that you would have to use a standalone template design, or create your own design.
Some examples of free standalone CMSes are:
If you want to build a more complex website, you will need to either hire a web professional or web professionals with skills in web design and web development, or possess those skills yourself.