If your marketing strategy includes paid search, the most common places are Google, Bing and Yahoo. If you have a higher budget you could also consider Ad and Affiliate Networks for casual sites.
If your marketing strategy includes paid marketing, the most common places to advertise are: Google, Bing and Yahoo.
If you have a substantial budget and are planning on creating a site on the adult network, you might want to consider advertising on Ad Networks or signing up to an Affiliate Network.
It’s worth keeping in mind that Ad Networks and Affiliate Networks will only take you seriously if you have a large budget. If you don’t, you run the risk of having your ad placed where the quality of traffic is poor.
To understand the Google advertising platform, please take a look at the Google Learning Centre. We'd recommend you taking the Google Fundamentals exam before entering into PPC advertising.