on the Ba.com website can you book multi stopped trips? how do you do this?
While you can (on the booking page, look for the link to "Multi-city/stopovers"), it's not a good experience - in general it will only give you a set of flight options without the price, until the very end. So it's quite time consuming to use.
Many people on the board start with
Google Flights which lets you construct a multi-city itinerary and search by price much more easily.