Think of it like a burger. You have a base that is the same for every customer. You can make small changes to this base (e.g. different dough such as multi-grain or sourdough). In addition, each customer can put together the toppings as they wish. Depending on preference and need.
This is also the case with our solution. You receive the standard product Dynamics 365 Business Central. We realize many projects in the standard solution – but sometimes small changes are necessary. And in addition, our customers purchase apps from us or our partners.