There are eight types of skill in total - you first select one and later choose a second discipline to make your specialty. The key is that you choose it all yourself. If you want to start out learning 'earth' skills, which give you access to fire magic and enable you to summon an earth elemental, but then add 'warfare' skills, which are all about physical offensive attacks, you can. You'll end up with a character that is uniquely yours.
You may have trouble deciding which two skill sets to cultivate, though. In addition to earth and warfare, there are the 'lightning' and cold magic-focused 'storm', as well as 'spirit', which enables you to steal life. 'Hunting' skills are based mostly around speedy, ranged attacks with bow and spear, and 'defence' gives you a better chance of deflecting or shielding off enemy attacks, or disabling enemies entirely.
Above: Age of Empires co-creator, Brian Sullivan, is the brain behind Titan Quest