In any MLM, you will find the organization split into two groups: the upline and the downline.
Your 'upline' consists of the people above you in the network. Whoever recruits you into the network is a part of your upline, as are the people above him or her. However, the person who refers you in is typically more accessible and often serves as a 'mentor' who trains you on how to work the program.
As you might have already inferred, you are a part of your mentor's downline. Further, the people you recruit into the MLM will be members of your downline.You might be thinking, “I can just find a program and join it without being referred by anyone, then I'll be at the top!” This, however, is not the case.
The absolute, top-tier of an MLM company's upline consists of the owners/founders, along with the first outsiders they brought in to the network.
So, while it is possible to be very high up the chain, you have to get in on the ground floor while the company is still in its infancy.
Now, joining a program late in the game and being further down in the structure does not mean you can't make any money, or any good money. There should be plenty of opportunity for you if the MLM is selling a legitimate product that people want and need.
That said, one of the things you should look for in any MLM you're considering is a product which can be sold to people outside of the network. In other words, you should be able to make some profit simply by retaining non-affiliated customers, as opposed to requiring your downline to buy the products.