Hi Kenneth,
SharePoint is effectively a CMS but a very expensive and resource intensive enterprise level one if that is all you are looking to use it for.
A common SharePoint farm usually consists of a SQL server, an applications server and at least one web front end server although. You could have this all running on the same box if you wanted to but I wouldn't advise it in production unless you had a very small user base (around 20). The platform itself is made up on Web Applications which are IIS websites that you can publish as an intranet/extranet/external website. Inside these web applications are Site collections which is a hierarchy of sites (of numerous templates - publishing sites, team sites, search sites, wiki sites etc.) that you use to lay out your content as well as to host lists that hold data and libraries that store files and documents. All this content is stored in the SQL back end within designated content databases which when used generally have a supported limit of 200gb. We currently use SharePoint as our intranet that students/teachers utilise as a VLE and admin staff utilise as a business management platform. Everything from HR policies, school calendars, to our estates help desk live there.
The whole thing came become an untameable beast though if it is not governed properly - I am currently building a brand new SharePoint 2013 farm to replace our 2010 farm due to the way it has evolved over the last 6 years. It was initially used to replace file shares so staff were advised to move all their content onto SharePoint, the original architecture that was put in before I started was not able to scale well and only one site collection and content database was created to house all of this (you can only have 1 content database per site collection). We quickly exceeded the 200gb limit and so much legacy and duplicate content began to appear which has cost implications on expensive SQL storage.
This is all related to the on-prem version of SharePoint though and there is the SharePoint online platform as part of office 365 which is a cloud based - making it a lot cheaper if you have a small number of users or limited requirements compared to SharePoint's capabilities. If you have any specific questions about your scenario, feel free to ask.