How to connect this circuit?? - Digital logic
Well, I'm not going to completely do this for you, since it looks like some kind of homework assignment, but I'll give you some hints and how I might approach it.

The start/stop button needs to work as a toggle, so that suggests that you should use the button to control the JK flip-flop whose output will gate the output of the 1 Hz clock going to the counter.

The 7493 is a binary ripple counter, and the assignment talks about using it to count down, so I would first of all connect the LEDs through inverters to the outputs so a counter value of 0 (reset state) starts with 1111 and counts down to 1000.  (Only three outputs are mentioned so you can ignore Q3).  When the LEDs display 000 the counter will really be 0111 so you can AND Q0, Q1, and Q2 together to stop the clock (i.e., reset the flip-flop).