The Triangle was thirsty, and it grabbed a glass of salt-water. It is a mixture, more specifically a solution where two substances dissolves into another.
Salt has high solubility when in water, it cannot be recovered and thus the mixture is homogenous.
The Water was the solvent which dissolved the solute which was salt.
If the salt didn't dissolve into water without it being recoverable it would be a heterogenous mixture.
The Triangle was disgusted and he decides to pick up some milk. Milk is a colloid where particles are equally distributed in a substance. That is what also makes milk a suspension If Triangle were to pour the salt water into it, it would dilute thus weakening the milk with a solvent.
Milk is saturated, unsaturated, or supersaturated. The salt water was a unsaturated solution where the solute completely dissolved into the solvent. If you were to put too much chocolate powder into the milk it would saturated where it exceeds it's capacity to dissolve. If you were to put way too much chocolate powder it would be supersaturated where the solvent contains too much solute.
The Triangle finished his milk and moved onto the orange juice. The orange juice is concentrated, where any diluting agent was removed.