You can see the full effect of Nature & Characteristic at Level 100, Nature raises it's positive stat increase by 10%, while decreasing the negative stat by 10%, eg. A Pokemon with Brave nature will have it's attack increased by 10% and speed decreased by 10% at lv.100. Charateristics shows your pokemon's highest IV, IV's are essentially a Pokemon's genes. They are determined when a Pokemon is caught or hatched, and cannot be changed through any means afterwards. What do IV's actually do? They influence stats (however, they are gotten onto your Pokemon much differently than EVs). Every single Pokemon you have has between 0 and 31 IVs in each of its six stats. You can only see your Pokemon's IV's full effect at level 100. So at level 100, one IV equals one stat point (it will be proportionate to your Pokemon's level before level 100, so a level 50 Pokemon with 30 IV's will have around +15 in that stat).
For more go to:
scroll down until u see 'IV Breeding'