Internet Service Providers (ISPs) are competing desperately to sign up customers, which has resulted in a need for middle men to sign up non-web surfers on behalf of the company, and/or attract customers away from their current service provider.
You'll either receive a payment per person you sign up, or will get a percentage of their subscription for as long as they use the service.
Finding new customers is not difficult. Word of mouth will generate a certain amount of custom, so inform friends and work colleagues; explain what they'll gain from going online, plus the benefits of your particular service provider.
Business customers will be more lucrative. Target firms likely to benefit from the Internet, attracting them via direct mail shots, leaflet drops, newspaper ads and articles.
Of course the easiest way of finding internet customers is to use the internet!