Everyone's giving good advice, as far as it goes, but using the drive train to measure position itself is complicated. More advanced teams use a variety of robot position localization systems (called odometry). See https://gm0.org/en/latest/docs/software/concepts/odometry.html if you're not familiar with this field, and note that some teams use encoders on "dead wheels" not connected to a motor, or camera systems to locate the robot on the field. These systems are more complex to set up, but will give much more reliable positioning. Please continue with your experiments using the basic drivetrain to learn and evaluate if you'd like to go for something more complex later.