Internet marketing is simply conducting marketing activities over an electronic channel, in this case, the internet. It comprises of your regular promotional tools used in a digital format.
Some of the more "internet specific" tools are:-
-Display advertising: using banner ads which helps increase product awareness
-Search engine marketing (SEM): promotes websites by increasing their visibility in search engine result pages through the use of search engine optimization techniques
-Social media marketing marketing on social media websites such as Facebook, LinkedIn, etc
-Email marketing: emailing commercial message to a group of people (which many a times reaches the spam so its not the best way)
These are just a few. There's a lot more information out there.