Search engine submission is the process of submitting a particular website to a search engine .
When You submit a website to a search engine the search engine may or may not index the contents of your website .
Indexing is very important for your site or blog to appear in search results.
Various popular search engines are Google, Yahoo, Msn etc. Submitting your site to these search engines will make your site appear in the search results in these search engines.
This will make a lot of people know about your website or blog and also increases traffic.
You can manually submit your site in these search engines separately, or you can make use of various free search engine submission websites like www.hit-counter-download.com.
Also see What is pinging?