Hey, I'm 19 and in college too.

I've got a high metabolism and my weight is watched pretty closely because I'm in a sport and I'm a stick. So this is what I do to keep weight on during season.

Eat three main meals a day. Breakfast is really important and I eat a huge pile of eggs and sausage or bacon every morning. For the other two meals, I'm on meal plan so I pretty much just shovel in whatever food is being offered
Just as long as you eat a decent sized meal you're fine. I always have soup with whatever I eat and a banana afterwards. Drink lots of healthy liquids-- water, gatorade, orange juice(or any juice), milk (I drink soy milk)-- with your meals and throughout your day! Smoothies are really good too if you are up to a little extra spending-- I get two a week with a protein booster.

Between meals, I snack... a lot. Granola bars, sport bars, trial mix, a sandwhich, crackers with something spread on them-- it's all pretty good. Just as long as you're taking in healthy calories.

Try getting lean cut red meats, beans, non water fruits, starchy vegetables, and heavy breads(spread something yummy on the bread too-- anything to add on the calories!) I also take daily vitamins-- haha just in case I get lazy with my diet somewhere.

Remember to exercise when you do this! That way you can gain some muscle too!
And make sure you don't gain more than a pound and a half each week either-- if you do, cut back just a little bit so you're back on track with healthy weight gain.