Apologies for the question as I am sure it is a very simple answer.. but how do tier points and avios from OW flights get credited to my BAEC account?

For example.

If a book a flight directly on AA or QR website can I add my BA frequent flyer number onto the booking? Will the corresponding avios and tier points automaticallly credit to my account?

Is it only certain flights that will earn tier points and avios from these OW flights? for example when I look at a potential fare on the BA site I sometimes get the choice to pick a AA flight so I just wanted to make sure that it is not just these flights that earn tier points and avios.

If I book a flight with a OW carrier through work and use CWT is the process any different?