Stakeholders are an integral part of a project.They are the end-users or clients, the people from whom requirements will be drawn, the people who will influence the design and, ultimately, the people who will reap the benefits of your completed project.
It is extremely important to involve stakeholders in all phases of your project for two reasons: Firstly, experience shows that their involvement in the project significantly increases your chances of success by building in a self-correcting feedback loop; Secondly, involving them in your project builds confidence in your product and will greatly ease its acceptance in your target audience.
There are different types of stakeholders and each type should be handled differently:
Executive stakeholders are the guys who pay the bills. Typically they are managers or directors who are involved with commercial objectives for the project.They should restrict themselves to commercial considerations and be actively discouraged from being involved in technical design, their experience and skills are vastly different to that of 'typical' end-users.
These are the guys that are going to use your product.No one knows more about what the product is supposed to do when it hits their desks than they do. No one! Including you! You may think you know better but if you don't listen to them you're kidding yourself.
Sometimes you need input from experts in other fields. People like graphic designers, support reps, sales or sometime lawyers and accountants.
I've also put together a short online course that describes project management fundamentals if you're interested in learning more about this profession.