I will not tell you why you need a web site as you are here.
I will only tell you important and not obvious issues of site building.
Let's start with web site technology.
If you do not bother this, looking as pure technical thing, one day your site developer can leave you (unfortunately everything can happen). And you will need to look for a new software developer. If your previous developer created a site using some exotic/difficult technology, in the worst case you will have to re-write a site.
I build sites using modern top-rated technology: CMS Drupal, many corporate sites are written on it. This is simple, robust technology, it has a huge community. It's simple to find a Drupal specialist.