Newbie Help

Since I started MFP almost a week ago I've noticed that I'm looking much slimmer especially my stomach area which makes me extremely happy because that is where I hold most of my body fat,unfortunately. (Inherited my grandma's humpty dumpty body) I'm awkwardly skinny fat to the point where sometimes people think that I'm pregnant because of my fat stomach and petite frame (3 kids) BUT I have noticed that my butt is getting flat as well I really don't know what to do? I'm guessing there's no way to lose the pudge and still build a bigger booty? There's so much SCIENCE behind all this it almost seems like an art.. it's a little mind boggling. I just need a simple plan that works that I can stick to. I've never weight lifted before and I'm intimidated but I think I'm ready to face my fears and join the meat heads over there in the free weights area of my gym. I typically run, walk, and do at least 20 minutes of intense workout on the stair master.. and im a waitress and mommy of a 3 and a 1 year old so im pretty much on my feet all day.any advice would be appreciated.