>According to the Project Management Institute (PMI), the term project stakeholder refers to, ‘an individual, group, or organization, who may affect, be affected by, or perceive itself to be affected by a decision, activity, or outcome of a project’ (Project Management Institute, 2013).
As a PM, I usually refer to the stakeholders as the people that requested the project, the people that pay for the project, and the people that need to be informed about any changes related to schedule, scope, cost, impediments, etc.
>What's the difference?
A Project Manager is rarely a stakeholder, though it could happen if the stakeholder is actually managing all aspects of the project.
It may benefit you to read the PMBOK and read some books on Agile and Scrum techniques. There are still many projects that use waterfall methodologies and are successfully on-time and on-budget. I was once a Portfolio Manager for a large insurance company in charge of data migrations from acquired insurers...there is nothing that stand-ups and scrum could have done to make the migration process any faster or better. Point: learn the basic methodologies first, then build on your knowledge. Agile and Scrum in the wrong hands can be terribly destructive. Knowing which methodologies may work best for different teams/projects/situations is key. Sometimes the overhead and bloat of Agile isn't necessary for simple projects. I once briefly worked as a subcontracted developer for a crappy consulting/recruiting company. The company wanted to "provide value" to the client by mandating that the client's IT Director and I had daily conference calls with the company's scrum master who only had 6 months of PM experience (I had 8 years of exp at the time). Which wouldn't have been unusual except I was the only developer, the IT Director wasn't involved other than "get it done" and gave two shits less about the daily stand-ups and agile process to design a 3-page site and a couple of forms, all of which had excellent requirements docs. I ripped through the work and got out of there in a week. Why apply such a ridiculous process/methodology to something so simple?