If I remember correctly, the ECG axis is the vector of ventricular depolarization. Basically, it's the route that electrical signals take through the heart. Deviation can be caused by abnormalities in the structure and/or function of the cardiac muscle. Deviation to the left can have a number of causes but there is a certain amount of variation in the normal population so I wouldn’t worry about it too much at this stage. Left axis deviation in the absence of any other signs of heart problems could simply be a normal variant. Unfortunately, if this is the case you might have to undergo a few other tests to conclusively establish that your heart is essentially normal.
I think that innocent left axis deviation is seen more frequently in short, stocky people and innocent right axis deviation is more frequently seen in tall, thin people.