1) Please click on the setup icon. Navigate to organisation then user groups.

Click on Setup >> organization >> User group.

2) Under the User group to be restricted please click on the manage icon. 

Click on the Manage ( gear icon ) as shown below:

3) Please click on the drop down menu under reports. Then disable the inventory and financials option.  Click on save. 

4) After Disabling - the Staff wont be able to access Inventory and accounting.