I looked in the forums and to what i saw there was not thread explaining how the natures work. So i have made a little research and came up with this information
Hardy: Does nothing
Docile: Does nothing
Serious: Does nothing
Bashful: Does nothing
Quirky: Does nothing
Lonely: +ATC -DEF
Brave: +ATC -Speed
Adamant: +ATC -SP.ATC
Naughty: +ATC -SP.DEF
Bold: +DEF -ATC
Relaxed: +DEF -Speed
Impish: +DEF -SP.ATC
Lax: +DEF -SP.DEF
Timid: +Speed -ATC
Hasty: +Speed -DEF
Jolly: +Speed -SP.ATC
Naive: +Speed -SP.DEF
Modest: +SP.ATC -ATC
Mild: +SP.ATC -DEF
Quiet: +SP.ATC -Speed
Rash: +SP.ATC -SP.DEF
Calm: +SP.DEF -ATC
Gentle: +SP.DEF -DEF
Sassy: +SP.DEF -Speed
Careful: +SP.DEF -SP.ATC
And a little bonus. These are also beneficial to a growth of a Pokemon.
Likes spicy = attack
Likes sour = deffense
Likes bitter = sp.deffense
Likes sweet = speed
Likes dry = sp.attack
Happily Eats Anything = does nothing
I hope this guide will help you become better a Pokemon trainer