89 Sunbird Speedometer Issue

Hello everyone, Ive got an issue with the speedometer on an 89 sunbird i just bought.
The pin is resting over under the 100mph instead of on the 0mph side, and it does not move when the car is in motion.
Someone told me to check the tact cable, unfortunaly i have no idea what it is or where it is, otherwise i would check it. So if thats the case maybe someone would be able to give me so slightly more in depth directions on that, other than 'check the tact cable' heh.

Thanks very much

Pete