New SEOs (Search Engine Optimizers) need to know the difference between on-page SEO and off-page SEO. On-Page SEO is the practice of building proper title tags, writing keyword-rich content, and writing meta-tags that are perfect for each page. Though this seems like a lot of work, it is really only the very basics of on-page SEO. Other important factors of on-page SEO are linking structure, outbound links, alt tags, link title tags, page shaping, and page design.
Off-Page SEO is much easier to understand, but generally harder to do. In general off-page SEO is link building or marketing on other sites to get links or get traffic. The only real reason for off-page SEO is to generate more traffic from other sites to your site.