SEO means search engine optimization. There are two parts of SEO. On page optimization and off page optimization. In on page optimization we do changes on website and in off page we do link building for website.
sumission is just to add to any site but always keep as per topic where you would submit your links. I recommend make 150 words an article because some place you need to add article on article submission directories.
you can submit to directories search engines etc.. but the best way to get noticed is to have high PR links pointing to your website, that way your webpage will gte picked up naturally by the search engines, indexed too... without a submission process!