Most of you know how google indexes your site - first it gets hold of your URL, or you feed it to it. Next, a spider visists your site, and it starts reading text from it, this excludes a few elements such as flash, javascripts,videos and images. It then copies the text to its main database and this is indexed later. It then comes back for more, crawls the links, then goes back again...and again...
Well, thats the activity of a spider in a nutshell. Things will be easier to SEO your site if you could see what the spiders see. There are some tools to help you out, and one is this:
Search Engine Spider Simulator