From:
https://www.pokecommunity.com/showthread.php?t=123757
"Natures are the final thing that effect a Pokémon's stats. If you want to find a good nature, pick a Nature that boosts the stat that a Pokémon uses a lot and decreases the stat that the Pokémon doesn't use very much.
Neutral Natures
Bashful Nature (Neutral)
Docile Nature (Neutral)
Hardy Nature (Neutral)
Serious Nature (Neutral)
Quirky (Neutral)
+Attack Natures
Adamant Nature (+Atk, -SAtk)
Brave Nature (+Atk, -Spd)
Lonely Nature (+Atk, -Def)
Naughty Nature (+Atk, -SDef)
+Defense Natures
Bold Nature (+Def, -Atk)
Impish Nature (+Def, -SAtk)
Lax Nature (+Def, -SDef)
Relaxed Nature (+Def, -Spd)
+Speed Natures
Hasty Nature (+Spd, -Def)
Jolly Nature (+Spd, -SAtk)
Naive Nature (+Spd, -SDef)
Timid Nature (+Spd, -Atk)
+Special Attack Natures
Mild Nature (+SAtk, -Def)
Modest Nature (+SAtk, -Atk)
Quiet Nature (+SAtk, -Spd)
Rash Nature (+SAtk, -SDef)
+Special Defense Natures
Calm Nature (+SDef, -Atk)
Careful Nature (+SDef, -SAtk)
Gentle Nature (+SDef, -Def)
Sassy Nature (+SDef, -Spd)"
I believe that should give you an idea of what natures do.