An autosurf is a website that allows you to gain traffic, or so those who provide it claim. It usually works as a traffic exchange, members gains points by visiting others sites and then they can spend the points to promote their sites. But you can also buy points to start immediately. The website will be visited via your internet browser or software during x seconds, depending on the owner settings, and then the system will automatically moved to the next site without any action required.
The main difference between autosurf and manual traffic exchange sites is that an Autosurf does not require any action from the user so your site might be viewed by a bot or the others user might not pay attention to your site. For example each 10 seconds a new website is visited automatically using your internet browser or website software. The advantage is that you will get more visits on your site and less work. Whereas using a manual traffic exchange site the user needs each time to click on a picture or a button or to solve a CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) in order to visit a new site. You will get real visitors and a better conversion of leads or sales on your site.
But, the thing is Google Ranking and Alexa use hundreds of parameters to position your website and nobody knows exactly what they all are. As both are very popular and trusted, it might be smarter to use more sophisticated software to generate traffic, such as Babylon Traffic. This quality tool allows you to increase your overall traffic and boost your SERP and Alexa ranking. Remember, traffic played a huge role in determining your value of site and there is no better tool to generate it then the mentioned one.