There are two bowls in front of you – one has salt and the other has iron filings mixed with sand. If I were to ask you to choose a bowl and separate its components, which would be easier? The second bowl of course – All you need to do is to take a magnet and keep it over the bowl to attract the iron filings and voila – you have separated them from the sand.
What about salt? Salt is made of atoms of Sodium and Chlorine. Sodium is a metal that reacts very readily while chlorine is a gas that is poisonous. However, they react to form sodium chloride which is common salt readily used even in food, and as you know the properties of this compound are totally different – salty, nonpoisonous, solid, etc..
With these two examples, I wish to introduce two terms commonly used in Chemistry – Compounds and Mixtures. Common salt is a compound while the iron filings and sand form a mixture. Let us understand them better.
Compounds are substances that are formed by the chemical combination of two or more elements by a strong bond between them. Sodium chloride is formed when Sodium and Chloride atoms interact with each other and bond strongly. The property of this resultant compound is much different from its individual constituents.
Other examples of compounds you may have encountered at home are:
Water – One oxygen atom and two hydrogen atoms combine together to form water, the elixir of life. As in the case of
salt, you can see that the properties of water are totally different from its constituent atoms of Hydrogen and Oxygen both of which are gases while water is a liquid.
Sugar is another compound made of atoms of Carbon, Hydrogen and Oxygen and I am sure all of you know that neither carbon nor hydrogen nor oxygen tastes as sweet as your favourite sugar.
With these examples let us move to the case of mixtures.
Mixtures are substances formed by merely physically mixing substances. They do not react chemically and retain the 
properties of their individual constituents. The iron filings and sand mixture is a fine example of this class of substances. The iron filings retain their property as does the sand and hence can be individually identified and separated with ease. Other examples include Air (mixture of gases like oxygen, nitrogen, carbon dioxide, water vapour, dust particles etc), muddy water (dirt and water/ sand and water).
To read more on the chemistry of compounds and mixtures:
https://www.chem.purdue.edu/gchelp/atoms/elements.html
https://bio.libretexts.org/@go/page/3741
