Hi and welcome to ECF. They both have a cone into which you jam that hollow mouthpiece/
tank.
It is refillable.
The big black cone screws off and at the bottom of it, there is a heating element with a spike that punctures a cap on the tank. This is supposed to allow the
juice to drip onto the heating coil.(atomizer)
In the ego-T, the cone and heating coil are all one piece. When the coil burns out, you have to buy the whole assembly. It is a one piece atomizer.
In the ego-C, the cone and the coil are two separate pieces. You replace just the coil (atomizer)
Because you only need to buy the atomizer, and not the whole cone, the C is the preferred unit.
The lesser of two evils, you might say.
Google "eGo-C and eGo-T" leaking- they are problematic. You won't find many vapers using them.