how to calculate initial rate from clock reaction?

Order of reaction:
You record the value of time (t) in the clock reaction for each different concentration.
Then calculate 1/t for each concentration. This is proportional to the rate of reaction.
Plot a graph of concentration against 1/t.

Based on the shape of the graph, you can get the order of reaction:
zero order - horizontal line
1st order - straight line, through origin
2nd order - upward curve with increasing gradient, through origin

Initial Rate:
t is the average rate of reaction for the first part of the reaction.
For this time, we assume the average rate of reaction is constant and equal to the initial rate.
So initial rate = average rate = concentration / time.
(Clock reactions are only accurate if less than 15% of the reaction has occured. Otherwise, the rate has changed too much so average rate no longer equals the initial rate.)

thank you so much for your explanation! much appreciated!!!

just to ensure i got it; so for calculating 1/t, i can just use the ‘time taken for colour change’ and then divide it by 1. then use those answers to plot a graph and from there i can see which order it is?

No. 1/t is 1 divided by the time. (If it were t/1, then it would just equal t).

Yes, t is the time taken for the colour change.
Yes, you use that answer (1 divided by time) to plot the graph.