I want to use it for my third year project containing 'animatronics'. I have a vague idea of what i want to do but my dads has been going on about relays and transistors and I'm slightly confused.
3rd year of what? I take it you are NOT a 3rd-year university electronics student, or you probably wouldn't be confused by relays & transistors. ;)
Have you done any programming or electronics before?
Like any project, take it one step at a time.
Like Shpaget said, try-out some of the examples. Or If you have some programming experience, start by looking at the language reference. At some point you should read-through programming language reference, but if you've never programmed before start with the examples or none of it will make any sense.
The two most important concepts in programming are loops - doing stuff over-and-over, and conditional branching - if-statments, etc., which is how comupters "make decisions".
I'd start your project with with the button Example... You push a button (a switch that you need to wire-up) and the pin-13 LED on the Arduino board lights-up.
Then, replace the button with your PIR (and/or "trip wires") and just make sure you can sense the movement and turn-on the LED.
Then, figure-out the drill-wiring. The Arduino puts-out 5 Volts, so you can test the drill and relay/transistor/MOSFET (whatever you decide to use) with a 5V power supply (or the Arduino's 5V power-pin) before you try controlling it actively with the Arduino.
Now that your input and output circuitry are working, you can connect everything together and turn-on the drill when someone trips the sensor(s).
If you need some more advanced programming, you can do that now that the hardware is fully-functional.