Aluminium is a metal that is placed in group 3 of the periodic table - which means that it has 3 electrons in its outer shell.
It has a fairly low atomic mass of 27 - resulting in it being a low density metal.
It has the very useful property of not corroding like iron does. You need have no worries that your aluminium ladder is going to corrode if you leave it out in the rain. In fact aluminium is a more reactive metal than iron and so you would think it would be more likely to corrode. It doesn't, because when it first reacts with oxygen it forms a stable layer of aluminium oxide that coats the metal and prevents any further reaction.
These properties of lightness (low density) and no corrosion make aluminium suitable for use in airplanes, ladders,soft drink cans, etc.
Aluminium is also one of the most abundant elements in the earth's crust, being usually found as either the compounds bauxite (aluminium oxide) or cryolite (a complex compound).
So why aren't all our cars made from aluminium - they would never rust and would be more economical because they would be lighter than cars made from steel (an alloy of iron)? It would also cut down on carbon emissions.
The answer lies in a point made earlier - which is the quite high reactivity of aluminium. The more reactive elements are, the more difficult they are to extract from their compounds.
Iron (used to make steel) is extracted from its ore in a process that dates back thousands of years. This process uses carbon to reduce the iron oxide to iron metal and works because carbon is more reactive than iron. It is a very cheap process because the energy that drives it comes from the combustion of the carbon to make carbon dioxide - carbon is readily available and cheap itself and is one of the reactants.
However carbon cannot be used to extract aluminium from its compound because aluminium is more reactive than carbon.
What has to happen instead is that the aluminium oxide has to be electrolysed. In this process, electricity is passed through molten aluminium oxide - causing it to split up. The positive aluminium ions move to the negatively charged cathode and accept electrons to become aluminium metal. This is a very expensive process due to the energy required to melt aluminium oxide and the large amount ot electricity used. In fact, in Russia they often have their own electricity generating power station on site.
This results in aluminium being four times as expensive as iron to produce. So that is why we don't use it to make cars - although a few models (expensive ones!) have been built - notably by Audi.
In most other respects aluminium is a typical metal, being conductive of electricity and heat, shiny and malleable.