If lots of different things are jumbled up together, we have a mixture.
Sea water is a mixture. It is mostly water, but it has many different chemicals in it, including salt. The salt is useful and can be separated from the sea water. The sea water also carries seaweed and sand with it. Often we could also see rubbishes around too. These can all be separated from the water.
Seaweed and sand can be separated from sea water by filtering. The seaweed and sand are trapped in the filter paper, and the water runs through the paper.
Filtering will not be separate the salt from the sea water, because the salt has dissolved in the water. When salt is stirred into water the salt crystals will disappear. They completely split up and mix in the water. A substance like salt, that dissolve is said to be soluble. A solution is always transparent (see through) even if it has a colour.
A solid dissolves in a liquid makes a solution. In a solution the liquid is called the solvent, and the solid is called solute.
Solute + Solvent –> Solution
Stirring water and flour makes the liquid go cloudy but soon all the grains of flour sink to the bottom. Flour does not dissolve in water. It is insoluble.