At 18 i was skinny as a rake always had a super fast metabolism.
after taking up weight training i also started eating like the world was coming to an end...
I would go to college with 10 sandwiches all with meat on, i would have 2 pints of semi skimmed milk while at college, along with multiple protein drinks-- i would literally constantly be eating, as soon as i had the slightest room n my stomch i would eat more--anything within reason-- weetabix, omlettes all sorts.-- i worked out i was drinking 10 pints of milk a day
pretty soon went from 10 stone to 14 stone within 3 years.

Im not saying thats what you should do though

like above-- stick to compound movements-- somthing like a 5x5 routine, write down your weights/sets and reps and aim to improve every session.
Eat some nice clean foods, meats, rice, potatos etc, ensure you have some protein with every meal and try and eat about 6 meals a day.
get a good quality protein drink and drop one of them before bed and first thing in the morning along with after you train.

You can get infinitely more complicated than that but thats a good place to slowly build into as a start.