Initiation - Getting it started. Defining what it is, what the expected outcome is, etc. Google "Project Charter". That's the end-product of the Initiation phase.
Planning - Putting together the playbook for the project before you set off to do it. Google "Project Management Plan". That's the end-product of Planning
Execution - Getting it done. Doing the work. Creating the outcome.
Closing - Turning over what you've created to operations, and ending the project.
Monitoring and Control too, but that covers the project from begin to end.
PMI has created the standard for the industry, and there are lots of books out there that can put more light on this.