What does a project manager do?

An engineer designs... a doctor cures... a laywer defends... a mason builds up. Ok, and what's the point in hiring a project manager

Is a modern organization, including all the necessary functions to develop a product or a new software, unable to coordinate a project execution without a PM in the staff?
And most important, why do people look puzzled at you while you try to explain what's your job?

Number 1. Project management did not take root centuries and centuries ago like other disciplines; enterprises felt the need to utilize a structured methodology to plan and execute the work since the nineteenth century only, with the advent of industry and of mass production. In other words, the majority of people is not yet familiar with this profession. That's it.

Number 2. Although people who manage projects know very well how many efforts are required to move things forward in demanding scenarios, it is next to impossible to elaborate in few words all the duties and the responsibilities of a project manager.

An acceptable definition sounds like the following:
In essence, the PM is the resource in charge to coordinate a team for executing a project in compliance with a given set of technical and quality requirements, a pre-determined budget and a defined time-frame to deliver. 
Doubtless,  in the current literature there is plenty of other equivalent definitions  of the role and of its variances.
The above mentioned one should find the majority of the professionals in agreement anyhow, as it encompasses the most common ideas about what a PM does.

As mentioned, a one-shot reply is hardly ever enough to satisfy the curiosity or clear the confusion of individuals interested to know what project management is about.
It is likely to see people left agape by the above definition and it is likely to be repeatedly asked to be more specific: "Well, ok...but in concrete, what does a PM do daily?!".

So, let's deepen it. As a project is an aggregate of deliverables to be achieved by different and complementary functions (engineering, manufacturing, logistic, quality etc) and being those functions, in turn,  an aggregate of human beings, we can try to provide a definition that sounds less academic:
project needs someone to coordinate resources, an individual who keeps the route and have the big picture of the project, without devoting working time to a specific and isolated task.
That's what a project manager does at the end of the day. S/he is primary a skilled resource, part of the permanent staff or hired ad hoc, who acts as a team leader for one specific project (sometimes more than one contemporary). 
S/he is responsible for the execution of each and every activity to be realized to deliver that project according to the requirements.
S/he spends the whole day in planning, monitoring, measuring, controlling, meeting colleagues and customers, deciding with the team where to cut, where to deepen, how to mitigate risks and to react to issues, which are the priorities and who needs to do what to maintain the project in good project health, not over budget and not under performing versus the stakeholders' expectations.
The more the project is large, the more extensive is the list of activities to be coordinated.

Project management is a fantastic profession, it can be very stressful at times. You may spend weeks hanging around the world to meet customers for challenging negotiations and the week after staying in the office to digest tons of emails, workflows and reports. You may spend days in preparing charts and flagging a to do list in the quiet of your confortable office, and all of a sudden be catapulted in the middle of a crisis to be managed in record time.

No matters where the project manager is, it is expected s/he is always - real time - aware of what is going on in the project. 
If something goes wrong, s/he is typically the first one to be put on the dartboard. On the other side of the coin, if the project is a success, her/his reputation and credit typically grow fast, regardless of who (in or out of the project team) or what (a tool, an economical situation etc..) actually failed or exceeded respectively during the project's development.

Last but not least. A significant part of the job is spent managing conflicts, inside and outside the team. Being a charismatic leader is a key for a successful project management career.

The project manager pad