It is hard to know where to begin. You wrote:

"You say in your diary that fingering isn't doing it but I don't know what fingering or doing it means please can you help."

"Can you" is obviously a question, so what sort of mark should go at the end?

You are quoting from the diary so what sort of marks go round a quote?

"Please can you help?" is a separate sentence and until you sort your grammar out I am disinclined to help anyway.

However, for all the other Traceys out there I will do so.

Fingering is what you do with your fingers while you use your mouth at the operative end of a recorder, covering up the little holes. However, I don't think that is what they were doing in the back row of the pictures, do you?

No I think Tracy had had insufficient thought for her own hygiene to allow Gavin to put his hands on her clitoris or allow him to put a finger into her vagina. The lamentable lack of washing facilities in the back row of the pictures is a problem here. Of course I doubt if Gavin exactly asked permission anyway.

"Doing it" can mean anything. In some cases it means doing IT, ie the lesson they were supposed to be doing when they were discussing fingering during Titanic. In this case they meant having full sexual intercourse. This is difficult but not impossible in the back row of the old Streatham Odeon but I have no intention of telling you how I know.