A very important component of a CPU is the clock. A clock is a component that "ticks" regularly to synchronize processing. A clock typically contains a quartz or other materials with well-known and relatively constant oscillation period, and the clock circuitry maintain and measures this oscillation to maintain its sense of time.
CPU operations are done between clock ticks and read/writes are done in the ticks to ensure that all components move synchronously and not trample into each other while in intermediate states. In our (2,3) Turing Machine, between clock ticks electricity passes through the logic gates to calculate the output from the input (I1, I2, R(t)); and in the clock ticks, the tape writer will write O1,O2 to the tape, the motor will move depending on the value of M, and the internal register is written from the value of R(t+1), then the tape reader will read the current tape and put charge into I1,I2 and the internal register is reread back to R(t).
Source: How Do Computers Work?
The quoted excerpt gives an excellent explanation on the mechanism of CPU operations.
But I have difficulty pinning down the sense of "in the clock ticks". I think a clock tick marks a point in time while the time between the clock ticks marks a passage of time. How does the tape writer write something to the tape in the clock ticks?