Technorati, blog aggregation and search services
Technorati is one of the principle services for syndicating blogs, searching blogs, indexing blogs, etc. It's a good idea to register your blog with technorati as well as the other similar services out there. Technorati provides many services so I'll try to cover them here.
Syndicating your RSS feed (see more here: Syndicating your RSS feed with Technorati): Syndicating your feed helps promote visibility of your site. Anybody who goes to technorati to search for blogs on a specific subject will have a better chance of finding your site if you proactively connect with technorati.
Using technorati to provide search (see more here: the Technorati Searchlet): Technorati is part search engine, and you can use that search engine from your site. On the page linked here you get instructions on adding a bit of code to your site that allows users to search your site. On requesting a search they go to Technorati's site for the search results, and the search results should come from your site only.
Your Technorati profile: Technorati allows a blogger to sign up and get a user id with their service. Once you're registered with technorati you can "claim" multiple blogs, and in general you'll have a "profile" page published by technorati that gives the public a short rundown on who you are.
The first step is to sign up with technorati. Simply go to their home page and click on the "sign up" link. They ask for a few things like your name and email address. Once signed up you can claim one or more blogs as being yours. The process is relatively simple but has room for confusion.
So, paste the code they provide into the template for your site.