A role is a named set of modules — whole sidebar sections like Purchasing or Warehouse. You grant modules to roles, then assign roles to people on the Users page. Manage it all at Admin → Roles.
Each row is a role, each column a module. Tick a box to give that role the module; untick to take it away. The change is live immediately and applies to everyone with that role.
The Admin column is special: it grants the ability to manage users, roles, and company settings, and it reaches every module automatically (so the other boxes lock on). At least one role must keep Admin, so you can't lock your company out.
A person sees a module only when both are true: their role grants it, and your company is licensed for it. Licence-gated modules (such as Loyalty) only appear in the grid once they're enabled for your company — so granting a module a tenant doesn't have yet has no effect until it's switched on.
The four built-in roles (Administrator, Purchasing, Stores, Warehouse) can be renamed and re-scoped but not deleted. To model something else — say a “Receiving” role with only Warehouse — add a new role at the bottom of the grid, tick the modules it needs, then assign it to people. A custom role can only be deleted once no one holds it.
Cost and margin live in the Purchasing and Reports modules. Roles without those modules don't see cost figures in the floor tools (item lookup, put away, counts) — keep that in mind when deciding what to grant a Stores or Warehouse role.