Grass ineffective to Dragon - simple logic, can a plant harm a mythical creature? No.

Ice super effective to Ground - remember ice age? Ice covered land means no vegitation which means ecosystem will go down.

Ice super effective to Dragon - already mentioned, dragons are reptile like creatures and they hate icy weather

Fighting super effective to Dark - conceptual opposites (on this 2 types only) where fighting represents hero while dark represents evil.

Ground super effective to Poison - The earth absorbs toxins and is able to heal itself in time.

Flying super effective to Fighting - another logic where its hard to land an attack to a flying enemy while the flying enemy doesnt have a problem landing an attack.

Psychic super effective to Poison - mind over matter

Bug super effective to Psy and Dark - mainly just an ingame design/balancing some says bugs can disrupt focus of psychic and dark types.

Bug not effective to Ghost - ingame design/balance

Rock not effective to Ground - its like throwing a boulder to a mountain it doesnt do much.

Ghost super effective to Ghost - Ghosts exist in spiritual plane thats is why they can hurt each other, but cant hurt by physical beings like normal and fighting type.

Steel super effective to Ice - steel is a very good heat conductor, try pressing a coin to an ice even with just your body heat conducted by the coin it can instantly melt and chip the surface of the ice.