Helios is designed to work around your business, letting you structure your data and workflow to suit how you want to run your business.
Helios is built around tiers and you can use this to divide up your business the way you need it.
In short, the Client is you, the customer is the physical locations of where you need your Staff be and when, and the staff is as written - it's your workers.
Your staff are all essentially employed by the client, and available to be used on all customers.
However you can employ a staff member directly under a customer which puts them on an exclusive list just for that customer. This is perfect if your staff need special training to work there - allowing you to list your trained staff as a separate resource when building your rotas.
You can also use different clients to separate out different departments if that is what you need- for instance, you could have a client that concerns itself only with your maintenance staff and a client that concerns itself only with your cleaning staff- and key individuals can be employed by both if they work across both departments. The choice is yours.