Hi @Patryk
Firstly, I should state - I am not an accountant. I always recommend that you run things such as this past your accountant just to be sure that it’s correct.
Secondly, I’ll try and go through your post an answer your questions.
You should enter the payroll journals on the date you submitted the RTI (Real Time Information) to HMRC.
In terms of entering the actual payment, the salaries, PAYE etc., there are quite a few topics on this already with examples - I’d recommend doing a quick search on the forums. But, this topic may be of some help to you.
I hope that helps!
[Edit]
I should add that in your case, if you submitted the RTI in December, you would log the journal then, but you can log the payment on a different date through your bank account (tag it as Salaries).