If you want a website that needs updating regularly, a Content Management System helps you do this.
You simply login, and then update the posts/section as and when you need.
For a static site - that is one that rarely gets updated (no more than 3/4 times a year - there may not be any need for a CMS. This is because it takes more time to build a site with a CMS than without. It may cheaper to have a static site and then have it updated by us when you need it.
However, a dynamic site - that is one that is constantly updating and pulling information from databases - would take a long time to update without a CMS.
We can advise you on whether a CMS would suit your needs.