I depends on a lot of thing.
A lot of guys will see how skinny you are and just start screaming at you to EAT EAT EAT LIKE A RETARD!
I don't believe in this line of thinking.
Weight gain should be just like weight loss, slow controlled and steady.
I think a surplus or deficit of 20% is healthy and safe.
So in your case you would take 20% of maintenance calories and add that to total.
Example: maintenance calories 2000.
20% of 2000 is 400.
So 2000
+ 400 = 2400 total
Now every 2-4 weeks you want to jump on the scale and weigh in to recalculate your cal total.
Example: lets say 4 weeks from now you have gained 10lbs.
You started at 145lbs now you are 155lbs so now you maintenance calories has gone up right?
So now just redo your math and add in the appropriate calorie amount.
Another thing to consider is body type.
Are you endomorphic, mesomorphic or ectomorphic?
If you don't know what these things are google and learn it will help you to understand your body better.
example: if you are endomorphic like me then you will want to strictly stick to the above mentioned 20% surplus.
But if you are ectomorphic then you can allow a greater surplus or even throw in some garbage calories.
Have you researched macronutrients yet?
Or how you plan on structuring your diet throughout the day?
I would suggest 50/30/20
Protein, carbohydrates,fats.
I would suggest "6 meals" for the structure of your diet.
6 meals divided evenly throughout the day. Just keep carbohydrates before 2 pm.
Hope this helps you bro