how to build a circuit that receivec a binary number (N) and square wave with cycle time ( t ) , and the output is square wave with cycle time (N*t) ??

 

Are you using a uC or discrete parts?

 

I've got an idea!
Use a counter (ie 74ls191) and feed it the clock. Take its output and compare ot with your input. Make a signal (use gates or a comparator) that responds to this equality and feed it to the load command input of the counter. Have the counter load the number 15 (by raising its input pins high).
As a result, your counter will start counting from 15 until the number you have given it (15,0,1,2...). Each time it overflows it will produce a pulse at the ripple clock output. Use this output for your new clock.
Refer to the 74191 datasheet for more information.