This page in a nutshell: Do not make changes to Wikipedia that will benefit you or anything you are linked to, unless you are sure that you are putting Wikipedia's guidelines and interests first.
A Wikipedia conflict of interest (COI) is when an editor wants to do something which does not help Wikipedia's goal, which is to produce a neutral, reliably sourced encyclopedia.
Changing pages to promote your own interests or those of other people, companies, or groups, is a COI. Where outside goals are more important to a user than building Wikipedia, that person has a conflict of interest.