Search engines use software to crawl as much of the web as is possible. The software is more commonly called a 'spider' or a 'robot'.

A Spider will work through the web by following links and stored information in an attempt to store details of every website in the world. They methodology they use changes every day and each search engine's spider's are different.

They visit a website, store, or cache, the information they find, then put the website in an index which determines the order results will appear in when a query is made to the engine. The trick is to move up the index by having the right content, people linking to your site and viewers liking it once they are there.

The spiders are very specialised and different to browsers like Internet Explorer as they don't download images and therefore worry more about the textual and navigational parts of your site. They are also very clever and spot attempts to 'fool' them like websites who add unnecessary words and excessive links. They still tend to like what a normal viewer would like.

As they are different to browsers in how they view a website they don't like excessive programming code, applets or confusing layouts. They appreciate simple websites full of worthwhile information. If they can't get to your site or it's content they will rate your site poorly.