Hey Fellas

I am I need of some help. I do not know how to diet or even where to start. I am 27 years old, i'm 5' 10" and I weigh 220, and i think my bf is probally in the 20's. I have always been small and very athletic. When I joined to military I weighed 140. I worked out pretty good when i was in. After I got back from spending 8 months in Iraq I got very depressed and gained a lot of wieght. Now that all that crap is behind me I really need to get the weight back off and gain some good lean mass. Some of my buddies that dont know any better told me that i just needed to get on some whinny and that would fix it , but after reading a lot of posts on here i found out that that wasn't true and that I needed to diet. I would like to get to around 12% bf and i know that I am not going to get there over night and I know that it is going to take some very hard work but i am ready. Somebody please give me some help!!!!