What is the real function of a web page?

Is it not quicker to simply advertise? I know SEO and so on helps, but that can take ages right? Also if you cannot afford a SEO expert , what are some simple tips to add automatic SEO to ones site?

Reason I ask is, I had a site, it was dead. Until I took out an advert then it got lively. So not being flush at the moment, why would I do both?