That is the store action.
The update action will get the id of the Supplier record that you want to update from the request such as suppliers/{supplier}, so the method accepts a second argument e.g.
public function store(Request $request, \App\Supplier $supplier)
{
// ...
In this example, because we have a wildcard {supplier} and a matching argument to the function $supplier that has a \App\Supplier typehint to the underlying model, we can leverage Route Model binding (i.e. the query to find the correct record is done automatically.