Creating an interrupt function with stm32f303 and ARMCC compiler

Hi all,

I am having difficulty in understanding "interrupts".
I am writing code for a stm32f303 microcontroller using ARMCC in Keil uVision 4 IDE.

After doing a couple of days of reading online and the compiler manual I have created
an interrupt function that looks like this:

////////////////////////////////////////////////////////////////////
__irq void TimerInterrupt(void) // located in the source file
{

.....statements....

}
///////////////////////////////////////////////////////////////////

///////////////////////////////////////////////////////////////////
__irq void TimerInterrupt(void); // located in a header file
///////////////////////////////////////////////////////////////////

Now, what I am trying to do overall is to have a interrupt function that will be called
when a timer reaches it's overflow and sets an interrupt bit.

Thankyou in advance if anyone has anything to contribute to this.

Sincerely,
Jim