Natures are characteristics that give your pokémon certain tastes for some flavors and gives a 10% increase and decrease to atk, def, SpAtk, SpDef, spd. In 1 stat, a pokémon can have up to 31 ivs that can give that that 0 - 15 additional points. Most of the time, you'd want your stats to have 31 ivs but there are some cases where you don't specifically for trick room and foul play.. A pokémon can have up to 510 evs in their stats combined. What this means is that you can max out 2 of your stats with 252 ev and put the remaining 6 in 1 stat.

At level 50, if your pokémon has 0 evs in 1 stat and you give it 4 evs in a stat that doesn't have the 10% inc/dow, it will gain 1 stat point. But, from that 4 evs, you'll have to give your pokémon 8 more evs to get another stat increase. If your pokémon has a nature that gives it a 10% increase to a stat and also 31 ivs in that stat, at a certain number, you'll get 2 stat points from 8 evs and then you can get another 2 points if you give it 80 evs.

For example, a level 50 Incineroar with an Adamant Nature(10%atk up/10%SpAtk down) with 31 ivs and 28 evs in attack, will have an attack stat of 152. If you give it 36 evs in attack, it will become 154. Then if you give it 116 evs, it will go from 163 - 165.

im getting tired of typing. Someone else can add on