There are many methods to promote your website. First of all your site should be search engine optimized with proper title, description, keywords etc. Use alt tags to all images and optimze its loading time.
Now your site is ready to get indexed by search engines by placing your site URL on high page rank sites and afterwards it needs promoting by writing articles,posting blog comments, using forum signatures, using google ad-words, paid text link etc.
Once your site develops fairly a good number of backlinks, there is no need of paid advertisement. It shall drive search engine traffic of its own forever.Beware to sell a quality product only.