How do online sales statistics collection services get information?

Question

Web traffic analysis

To collect information, we transferred one referral link.
How can you track the channels of attracting traffic by one link, posting it on YouTube and Facebook?

Answer 1

The page (server and scripts) collects the referrer from the link (where you came from)
Plus, if 'you are a large network' you may have some analytical scripts that clients already have (browser plugins, advertising banners, counters, pixels, subscription buttons like social networks and other things) - this is the user ID, where he goes (from the list of those services who have these scripts), when, whether he buys something, etc.
Also, large ones conclude agreements on the exchange of information whether they buy it stupidly, there are a lot of options. For example, bases of wifi clients that use free ones in one place and meet in another (also connect using a bunch of parameters).
This is a whole world, collecting information about customers and analyzing it.

Answer 2

Links for each channel of attraction should be different, then it will be possible to track.
Some unique component is included in the link

Answer 3

How can you track the channels for attracting traffic by one link, posting it on YouTube and Facebook?

- for example, the site engine is configured so that when www.site.ru/?source=ref-vasya gives the visitor a special cookie, and then having this cookie in the user's browser, you can track anything.