The ticks give you rate of travel for left and right wheels. A hundred times a second, convert this to movement and rotation of your robot. Keep accumulating position each time you do this. There's a bit of an art to getting enough readings from the encoder between each sample interval, so that you don't get lots of noise/jitter, but don't wait long enough between each interval that the uncertainty of when exactly you were turning within the interval becomes a problem.
If your motor gives you 6000 ticks per gearbox output shaft revolution, as an example, and the diameter of your wheels is 100 millimeters, then you know each wheel travels (100*pi)/6000 millimeters per tick, or about .05236 millimeters.
Now, if you get 62 ticks from one wheel, but 59 ticks from the other, you know that the wheels have been traveling 32.4632mm and 30.8924mm respectively. Now, find two circles whose difference in radius is the wheel base of your robot, and whose arc length at the same degree of travel is these values; find the center circle between these circles, and use that same arc length, and that's the path your robot has traveled.