Well, Hunter, welcome to the WG forum.
There are plenty of tips to gaining in various threads on here, so I won't repeat them - just my own three points:
1 - weight goes where it wants to go, it's genetic. Eventually it goes everywhere but you might start with a *** and no belly, or thunderthighs and skinny arms, who knows?
2 - slightly facetious this, get older

it is difficult (but not impossible - there are plenty of exceptions) to gain weight young because of lifestyle and metabolism. Once you hit your mid 20s and the metabolism slows down, combined with driving instead of walking or cycling and a sedentary job, the pounds will pile on.
3 - finally, and most of all, alcohol is your friend. Most beer/cider/lager contains about 200 kcal/pint (more for things like Guinness or real ale), and it's all empty calories, so you still need all the usual nutrients. In addition, drinking usually leads to snacking on salty, high-fat foods like crisps/chips, peanuts, pork scratchings and pretzels. Finally, rolling home half-cut from the pub, a greasy kebab or pizza always seems like a good idea!