Database design

I have a [Employee] who belongs to a [group] and works on a constraction [Site] using a certain [Tool]. The employee can move to a different group and a Tool can be assigned to a different person.Employee can have multiple tools. Also, we rent the tool from a company that charges us per hour usage. So we receive a [bill] monthly for an [Employee] of certain [group] using certain [Tool]. My attempt for the first part is as follows but I am not sure. I ask help for where to start.

Employee-->EmployeeGroup<--Group | EmployeeTool | Tool

I receive the following pages for the bill

invoice {each line contains group summary} InvoiceSummaryPerEmployee{each line contains an emplyee of certain group using cetain tool) InvoiceToolUsage{hourly usage of a tool, including, chares, taxes etc)

-the InvoiceToolUsage contains hourly mutple lines per tool -InvoiceSummaryPerEmployee contains total lines of each tool used by employee in a group -invoice is group total

Thanks