The materials needed for the project can all be found at Tayda.com. It is a semiconductor store in which most things are not very expensive, but are very reliable. You do have to create an account, but they are trustworthy, so go ahead.
Step 1: Getting Started Using Fritzing
Fritzing is a prototyping application (not a prototyping simulator) that I use to plan or record a project. Go to http://fritzing.org/download/ and download the fritzing prototyping application. After you download it open it (on a mac it will be under downloads). Find the Arduino Uno part under the core parts section and drag it to the breadboard.
Step 2: The Timekeeping Circuit
Find the DS1302 IC in the core parts section and drag it onto the breadboard. Find the crystal part (in the core part section) and drag it to the breadboard. Conect it in between the DS1302 X1 leg and X2 leg. Connect the +V pin on the DS1302 rtc to arduino 5 volt pin. The crystal helps the rtc module keep track of the time. The rtc module keeps track of seconds, minutes, hours, days, weeks, months, and years.
Step 3: The Backup Battery
Click the search button in the fritzing part selector. Search LilyPad Coin then drag the first result to the breadboard. Connect the positive side to the Vbat (backup power) lead of the rtc IC and the negative side to the ground of the rtc.
Step 4: Connecting the Circuit to Be Read by the Arduino
Next, connect the CE (chip enable) pin to Arduino digital pin 5. Connect the I/O SPI data pin to Arduino digital pin 6. Connect the SCLK (SPI clock) pin to Arduino digital pin 7.
Step 5: Choices, Choices, Choices
Now here is where you get choices, if you have a little over $30 and want to make this project a shield keep going, if not, build the circuit on a breadboard and use the example code (on the last step) to program your clock. If you want to make the shield follow along with the instructable until the end.
Step 6: Making the Shield
Go to http://fab.fritzing.org/how-to/pre-fab for instructions on how to make the shield.