A technician is someone who has knowledge and training in a technical process. If you are having trouble with your computer network, you might have to call in a network technician to get it sorted out.
A technician knows all of the ins and outs (the technicalities) of a specific process. A computer technician knows all about how computers work and how to fix them. Likewise an automotive technician (a mechanic) knows all about cars and how to fix them. Technician is not always associated with technology. If a painter or a musician is trained in various artistic, or musical techniques, he or she can also be called a technician.