Because the add-in is basically an API wrapper, every generic function's first argument is (almost) always the endpoint to which a request is sent, including query string parameters. Subsequent arguments depend on multiple factors: the function and its method (GET, PATCH, PUT, etc.), and which endpoint the request is sent to. Endpoints returning data require fields to be specified in order to populate output arrays (see Data Model). The Formula Builder is a useful tool for exploring the correct syntax for function arguments.
Wrapper functions, such as the included trading functions, require specific arguments detailed in the Insert Function dialog:
Which can be entered in the screen that appears when this function is selected:
Using these wrapper functions outside of VBA is not advised, as these will send a order/cancellation/modification directly to OpenAPI when the 'OK' button is pressed (and all fields are entered correctly).