Startup sequence for lpc1343
You don't need to do anything to start the clock, and it's not necessary to start the PLL in order to blink an LED. By default the processor wakes up running at 12 MHz, using the internal RC clock directly. As long as that's a fast enough clock for your purposes you don't need to do anything else.

The manufacturer (NXP) is not at all vague about starting the clock and PLL. There is C code to do this in the system_LPC13xx.c file that comes with their examples (at least with the LPCxpresso examples). The clock is configured in the SystemInit() function.

Update: If you are using the lpcopen package, look for clock_13xx.c