To begin with Search Engines and website optimisation are not the same, neither are SERPs (Search Engine Results Pages) or SEO (Search Enginge Optimisation) and online marketing cover all of these and much much more.
All are closely related in some way though.
I am not going to try and explain the subtle differences on a single page, this will be good for the sites website optimisation and hopefully help its SERPs.
If you are looking for someone to maximise your online marketing exposure, I can highly recomend Mark Vassiliou at
Search foundry, Mark's knowledge of pay per click management and
search engine marketing is massive.