HYIP which stands for High Yield Investment Program is just what it sounds like, a program offering a high yield investment. HYIP's are offering probably the most profitable investments available today, much more than any bank or investment fund.

Autosurfs - are a similar type of site to hyips, but in order to make the ROI on your deposits, you must "surf" a pre-determined number of websites to receive you daily ROI (about 5 to 50 daily).

There is risk in any business. If you can't take risk than you can't expect to gain high profit. These HYIP companies manage their investment in high risky arena and that's why they also make high profit.

Simple and straight answer: You don't. You can take advice from people in the industry, read forum posts. The decision to join should be entirely your own, and you should understand the risks involved.

Most HYIP’s use different type of e-currency as the way of accepting funds from investors. Nowadays Liberty Reserve is the most used e-currency but there are also other e-currency such as Perfect Money, Alertpay and many other. E-currency has become a very popular way of exchanging money online. It is also used by various merchandise websites as payment method. 

It depends entirely on how much you invest (obviously the more you invest, the more you make), and the daily percentage of the program (higher daily percentage = more money daily).

Again, you can lose as much as you invest. Therefore remember the golden rule of HYIP: 

ONLY INVEST WHAT YOU CAN AFFORD TO LOSE.