Since you already got trainer, I think he'll help you out for your training part.
Your eating part is the one you must cover yourself. Like what janson said, NEVER skip meals. For skinny people should be eating 5 meals a day.
Basically the rule is to never feel hungry.

If you ate at 7pm, and you sleep at 3am and you feel a little hungry but lazy to cook so you go to sleep, that also consider hungering yourself. I know because I was like that too