What it means
Search Engine Optimisation (SEO) is the industry that "optimises" your website to make it appear as high as possible on the Google search listing.
One of the techniques that SEO companies use is to pay other sites to link to yours.
How to do it - the best and real way
The best way to increase your ranking in Google is to have:
- good content
- regularly updated content (like a blog)
- the basics correct (eg page titles)
Methods of "tricking" the Google system may work in the short term, however Google are constantly tuning their ranking system.
Just to repeat, the most important thing that you should do is have good real content, updated frequently.