Ok pin 13 would be pin 5 on port B on the actual chip.
Fastest way to turn it on is sbi(PORTB, 5) and to turn it of its cbi(PORTB, 5).
Just like assembly. 
Those two are defined in wiring_private.h and are pretty simple.
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif