This is about on and off led system.
Here we can on and off the led by touching a particular part of circuit.

Step 1: Requirements for Making Circiut

Things needed are:
1. Breadboard
2. 555 Timer IC
3. Some wires
4.LED
5.100 Ohm resistor
6.4 pins (As touch plates or anything which can conduct electricity)
7. 9 volt battery with battery clip

Step 2: Steps for Construction

1. Connect 555 Timer IC as shown in figure .
2. Now let's assume upper part of breadboard as positive part and negative part of breadboard as negative part.

Step 3:

3. Now connect a Wire from positive side of breadboard to the eigth (8th) pin of IC as shown in figure.

Step 4:

4.Connect another Wire from negative side of breadboard to the positive side of IC or first (1st) pin of IC as shown in figure.

Step 5:

5. Now connect another Wire from 8th pin of IC to 4th pin of IC as shown in figure.

Step 6:

6. Now connect anode of LED to the third pin of IC and cathode of LED to the blank space on breadboard as shown in figure.

Step 7:

7. Now connect 100 ohm resistor from first pin of IC to the cathode of LED as shown in figure.

Step 8:

8. Now connect touch plates or any other pins which can conduct electricity as shown in figure.
Connect touch plates from pin 1 and 2 of IC and pin 8 and 6 of IC as shown in figure .

Step 9:

9. Now connect 9 volt battery as shown in figure.
Connect positive end of battery to positive part of breadboard and negative end of battery to negative part of breadboard.