Just like what James has explained, you earn commission
by sending visitors to the owner's product site with your
affiliate link, and when the visitors buy the products,
you get the commission.
The most reliable & successful affiliate program is
Clickbank.com , you can become a free affiliate and
promote thousands products in different fields
There are many types of affiliate program, e.g. 1 tier
2 tiers or multiple tiers (like network marketing/MLM)
Clickbank.com only offers 1 tier affiliate plan.
For 2 tiers or multilevel affiliate program, you can
earn money from your sub-affiliate/downlines efforts,
which mean if your downlines get the sales, you are
also eligle to earn some commission!
And, there are two types of pay plan, one time or
monthly residual. If the product you promote is a
subscription based, then you can earn the residual
income each month as long as your customers renew
their membership every month ... this is the income
source I love as I only do one time job and get paid
every month (that's the passive income!)
Earn Passive Income From Internet!