NOTE. If you're line training then you are a fully qualified, appropriately licenced pilot on that aircraft type. All you're doing is learning that airlines procedures. My comments below assume you're an FO.
DUAL
You only need to use the dual column for your circuits as you're not yet properly qualified and you're receiving instruction.
P2
All flight where you are PM are logged under P2 whether line training with a safety pilot, without a safety pilot or normal line flying
P1/S (or P1 u/s)
Where you are PF you use the P1 column but use either of the above annotations. Once you start command training then ALL your flights go under P1/S until you have passed the final line check, thereafter, obviously, you log it as P1.
As an FO, by using the P2 and P1 columns (assuming you log each flight individually) then you can see at a glance who was PF/PM. As a captain, I note PF/PNF in the remarks column in respect of myself incase a need to refer back.
Instrument time can be logged while you are PF but would only be the flight time not the block time.
Night flying as PM also fully counts towards your total night hours required for the ATPL which I reckon is a marvellous arrangement!