So explain to a relative neophyte what that actually means in English please?

When we click through to a BD link, because IB is an affiliate, do they get $$$ for the referral? Or do we need to actually purchase from BD for them to do that?

Is it like quidco, where the referring site (i.e. quidco) gets a kickback from the company from which you purchase the stuff - only of course quidco shares that kickback with its members whereas presumably IB would retain that?