What is this custom search about found it hard to understand. Please can some one help found it complicating.
Are you talking about how you can set the Google search to search specific websites instead of the entire website.
The custom search helps you focus the search on a specific topic. For example, you can have a custom search on "Immigration" and google will focus on searching pages within the topic of "immigration".
If you know what to do you can set that a custom search will show you website as number one, in a search in you topic.