Type Matchup Chart Explained

Water --> Fire: Water douses fires
Water --> Ground / Rock: Erosion

Fire --> Grass: Forest fires
Fire --> Bug: Magnifying glass on ants
Fire --> Ice: Heat melts ice
Fire --> Steel: Smelting

Electric --> Water: water conducts electricity and kills fish
Electric --> Flying: Birds get zapped by lightning (?)

Grass --> Water: Plants drink water
Grass --> Ground/Rock: grass cracking through stone/earth; living in the earth and absorbing nutrients

Ice --> Grass: too cold for plants to grow / cold snaps kill plants
Ice --> Flying: birds migrate due to the cold
Ice --> Ground: ice expands into water and breaks the ground (?)
Ice --> Dragon: dragons are cold blooded and are weakened in the cold

Bug --> Grass: bugs eat grass
Bug --> Psychic: insectophobia is very common
Bug --> Dark: bugs transmit diseases to poor (black) people (?)

Poison --> Grass: Toxins cause plants to wither and die
Poison --> Fairy: Poison kills the prince/princess

Ground --> Electric: ground doesn't conduct electricity
Ground --> Rock/Steel: earthquakes can rupture structures
Ground --> Poison: ????
Ground --> Fire: dirt and earth can smother fires

Fighting --> Normal/Rock/Ice/Steel: Can punch through anything
Fighting --> Dark: honest fighting beats dirty fighting

Psychic --> Poison: inventing medicine
Psychic --> Fighting: brain over brawn

Flying --> Grass/Bug: birds eat seeds and bugs
Flying --> Fighting: It's over, Anakin. I have the high ground.

Rock --> Fire: rocks can smother fires
Rock --> Flying: two birds with one stone
Rock --> Ice: rocks can smash through ice
Rock --> Bug: rocks crush bugs

Ghost --> Ghost: ????
Ghost --> Psychic: phasmophobia is very common

Dragon --> Dragon: only the strongest can beat the strongest

Dark --> Psychic: Nyctophobia is very common
Dark --> Ghost: Darkness consumes the undead (?)

Steel --> Rock/Ice: Steel can smash through both

Fairy --> Dragon: Knight slays the dragon
Fairy --> Fighting: Fighters have bad will saves
Fairy --> Dark: Good guys always win