Basically there are two types. Manual surfing and Auto surfing. Some Traffic exchanges cater for Manual surfing only, some cater for Auto surfing only and some cater for both.
Manual surfing - This requires your input by clicking a button after a specified time period, generally 15, 20 or 30 seconds, although there are a few other variations. With manual surfing, the surfer is expected to view each site. However, with most exchange sites, it is possible to minimize or resize the windows. This defeats the purpose because it allows multiple sessions to be run simultaneously. On the better exchange sites, security measures are often used to deter this. These are normally random prompts that require user input. For example, after x number of page views, you may be required to enter a code, select a color or image or perform some other variation of this.
