I assume you refer to petroleum, which as a fossil fuel, is a source of energy. Energy is needed to generate heat, to drive machines and to allow transport, for example when it is used as a fuel for planes.
The economic importance of oil is that energy is needed to produce all goods and oil or other sources of energy are indispensable: owning energy sources produces riches. The political importance is a result of this: politicians and powers are strong if they have a strong financial backup, and this can be provided by having access to an energy source.
Similarly the social importance is based on the economical wealth oil brings: it allows for a development without financial fears for those who control it, but also creates differences based on wealth disparity.
