WebmasterQuery

Google crawls your site and then adds your content to it's database. This is how your site is indexed. Most people care about how it is ranked rather than indexed though.

As far as I know it happens automatically after your site is live. It can be easier to have your site indexed in Google if you have keyword-specific content on your pages that is well-written. I know also it helps when you have blogs that allow you to add tags to the posts. The content that you post is what Google finds and indexes.