Search engines and their crawlers/bots automatically and periodically checks your site. The more your site is updated, the more it is checked by the crawlers. You need the backlinks to your site too. But what can you to do if you started with totally new website without backlinks? How could the crawlers find your site? There is a simple answer. Submit your site to the most known search engines manually.
Submitting your URLs to the small search engines and catalogues is time expensive. But it can help too, when you need to build some backlinks. Submitting to the biggest search engines is a matter of success. Usually you need to submit only once, because the crawlers will then check your site automatically in the future. So, there are submitting forms for the four biggest search engines:
Why Submit??
I think the best thing to do is not even submit, let them find you from links on other sites. Build as many backlinks as you can and you'll be indexed in days.
indexing
I agree, don't bother submitting, it will take months sometimes. Use backlinks from other sites to get noticed, use well known social sites.