Steel type pokemon take double damage from Fire, Fighting, and Ground-type attacks. They are immune to Poison-type attacks and will only take half damage from all other attack types except for Water and Electric-type attacks, which deal normal damage.
Steel-type moves deal double damage to Ice and Rock-type Pokémon. However, they only deal half damage to Fire, Electric, Steel, and Water-type Pokémon. They deal normal damage to all other Pokémon types.