For example, if someone promotes their Ledger ref link, they will get 10% for each sale which is $6.5 for each Nano S, or $16 for current Ledger Bundle Pack (S+X model). For those who create their own web pages and know how to promote them, affiliate business is one of the options how to start making money.
Affiliate links are also not for everybody. I've posted myself ref links for Ledger here and there, but nobody bought from my referral.
I think that has to either be some kind of influencer, either have a blog that's read a lot.