Usually, on most sites, it works like a pyramid. This example is three levels deep.

You are on the top. If three people would sign up by using your link there would become three people below you.
You would, every time they would do anything, get a part of that based on a percentage.
If one of those three people would get two referrals, you would have the same.
But it is an smaller part of their earnings.
Even if one of these people would get an referral you would earn an even smaller part from him.(except when it is one level deep)
This is by three levels deep. If it would be 5 levels deep you can understand the earnings would get even better.

But even if it would be three levels deep, there is no limit on most sites on how many people you can refer.
The first level is the only one which you can make bigger.
The other levels depend on what your referrals are doing.
But as long as your referrals, all of them, are doing something, you will get a percentage of their earnings extra on your account.
This doesn't matter anything for your referrals, it only profits you and doesn't cost them anything.

So the best thing to do is get a lot of referrals and try to make sure they get referrals too.
This would be a good start.
And by the time you have done all of this you know enough to continue your path on the internet marketing road =D.

Example with Bux.to:
You are a free member with 10 friends.
Each friend clicks 15 ads a day.
15 x 0.01 x 10 = 1.50$ a day.
Each week you earn 10.50$.
Each month ± 45$.
But you think it isn't enough. You get a 100 referral pack.
But not all are active so from 15 they get 10 clicks.
10 x 0.01 x 100 = 10$ a day.
7 x 10 = 70$ a week.
Each month ± 300$.
But you also had your 10 friends.
So 11.50 a day, 80.50 a week, and 345 a month!