This really is the easiest thing on the planet, so why do so many PPL candidates f**k it up? More to the point are instructors really that sh*te that they can't teach their PPL students what to log? If I were the CAA I'd haul them up in front of me and want to know WTF they can't teach people to do it properly.
So just to summarise what has already been said 10 times:
With an instructor: P/UT (Under Training)
With an examiner, and you pass: P1/S
Solo or none of the above: P1 (PIC or whatever)
Even after your PPL is issued, the above applies in general.
There, difficult?