Let me quote Wikipedia ("555 timer IC," Wikipedia: The Free Encyclopedia, June 21st, 2015)

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in one package.

Introduced in 1971 by American company Signetics, the 555 is still in widespread use due to its ease of use, low price, and stability. It is now made by many companies in the original bipolar and also in low-power CMOS types. As of 2003, it was estimated that 1 billion units are manufactured every year.

This instructable will show you how to make a square-ware generator module from a 555 IC. A square wave is defined by its frequency and its duty cycle. The frequency is the number of cycles per unit of time and the duty cycle is the fraction of each cycle taken up by the high state. By changing the passive components of this module, it is possible to adjust the properties of the generated square wave. This module has a 3-pin SIP small footprint. The layout figure was produced using DIYLC.

You can see in the circuit figure that the 555 IC does not produce square wave out of the box but requires some wiring and passive components (image credits). This can be easily done on a breadboard, but in the end it is certainly nicer if packaged into a small 3 pin module.
In this instructable, I used values of R1 = R2 = 10 kΩ and C = 47 µF. This will generate a square wave of 1.023 Hz (almost 1 s cycle) with a duty cycle of 66.7% (2/3 of the cycle time will be high and 1/3 will be low). If you want to calculate values for a different square wave, I recommend the following online calculator: 555 astable calculator.

Step 1: Parts

This project can be made using very inexpensive parts. Most likely, shipping will cost your more than parts...

As explained in the introduction section, you can change the value of the 10 kΩ resistors and the 47 µF capacitor to suit your needs. You may therefore consider buying bulk quantities of resistors and capacitors of various values.

Step 2: Cut the Protoboard

Cut a 5 x 7 piece from the protoboard as illustrated using a Dremel equipped with a cutting disk. Make sure you cut it in the right orientation. Using a cutter, cut the first four traces as illustrated. Do not forget that you see the board upside down when you make this cut as opposed the layout image in the introduction section.

Step 3: Solder and Add Components

Start by soldering the wires, SIP sockets, 3-pin header and 10 nF capacitor in place. Then insert the 555 IC, resistors and electrolithic capacitor in their respective sockets. Respect the polarity of the electrolithic capacitor. The negative pin of the capacitor should be connected to the top left trace.

Step 4: You Are Done!

You are now ready to use you new square wave generator module. According to the datasheet, the NE555 supply voltage should be between 4.5 and 16 V. Also, you should not try to pull more than 200 mA from the output pin. Pinout from left to right is as follow: Out, Vcc, Gnd.

You can see the module in action with the output pin connected ground via an LED and a 1 kΩ resistor.