Help on buying stock?

I'm 16yrs old and have been interested in buying stock in companyes i dont have much money (about 300) should i buy into bigger companys such as ATT with the new iphone coming out and them just buying out t-mobile? or should i buy in MCD or some cigarrette company? please give me ideas or tell me who you have bought from if you feel okay with it and i would apreciate it if you told me why you bought from them and how much the stock was. Also any companys i should stay away from?