If you have never played a piano before, it is a good idea to familiarise yourself with positioning your hands on the keyboard. Just like with typing, if you position your hands properly over the keyboard, you will find that you can move your fingers quickly and accurately over the keys of a piano How to Position Hands on a Keyboard Pianokeyboard without looking at the movement of your fingers. This allows you to look at the sheet music rather than your hands. More at http://funkelixo.com/blog/view/16045/discover-the-best-pianos-for-children.
When you position your hands, you should number your fingers in your head. Some people like to write numbers on their knuckles when they are beginning to learn as this also helps remember which number each finger is. Numbering fingers helps you to note down finger placement instructions on sheet music.
Your thumb is number 1 and then each finger after that is 2. 3. 4 and 5. This is the same for both your left and right hands.
When positioning your hands on the keyboard, you should start with your right hand. Ensure that you place your thumb on middle C. Middle C is the C note that is most central on the keyboard. From here, your index finger is placed on the D key, the Middle finger on the E key, the ring finger on the F key and the pinky goes over the G key.
To position the left hand, again, you should start with middle C. Now, you should place each finger beside it just as you did with the right hand. Your index finger will rest on B, the Middle finger on A, the index finder goes on G and the pinky goes on F.
When you are playing scales, or playing a number of consecutive notes, you would press down the thumb, the index finger, the Middle finger and then pass your thumb under your middle finger and press your thumb on the next note.