Good question!
There maybe as many answers as there are counsellors.In the simplest terms 'counselling' forms a safe relationship which you can use for your growth. We are hurt in relationship with others, and we are healed in relationship with others.
Sometimes Campbell uses the following metaphor to describe an aspect of counselling to his clients:
"The counselling hour can be a bit like a laboratory - a safe place where you get to experiment with new or different ways of being you. It's safe because dangerous elements, such as controlling people, hurtful situations, toxic relationships, triggering circumstances, judgement, time and responsibility pressures, have been removed. In such a safe place, with warmth, honesty and empathy, the fear of failure can diminish and the 'real you' can come forward.'New or different ways of being you' could include new ways of; communicating, feeling, responding, reacting, relating, loving, perceiving the world and those around you, behaving, defending and being vulnerable. When you have experienced 'new ways' of being you and are comfortable with them, you can start to take them from the laboratory, and out into the rest of your life." 
Ruth reflects:
"One way I explain the importance of paying attention to our 'inner world' is through the metaphor of cars and mechanics. For those of us who don't have much understanding or experience in fixing cars, it seems totally natural and normal to take our car to a mechanic when it needs some work. In the same way, when we notice we aren't 'firing on all cylinders' in an emotional way, it makes sense to check in with someone who can help us figure out what needs to happen for our mental/emotional health to improve."