Language is the whole system of language that precedes and makes speech possible. A sign is a basic unit of langue.
Learning a language, we master the system of grammar, spelling, syntax and punctuation. These are all elements of langue.
Langue is a system in that it has a large number of elements whereby meaning is created in the arrangements of its elements and the consequent relationships between there arranged elements.
Parole is the concrete use of the language, the actual utterances. It is an external manifestation of langue. It is the usage of the system, but not the system.
By defining Langue and Parole, Saussure differentiates between the language and how it is used, and therefore enabling these two very different things to be studied as separate entities.
As a structuralist, Saussure was interested more in langue than in parole. It was the system by which meaning could be created that was of interest rather than individual instances of its use.
Subject + present from of the verb .......Langue.
Prime Minister goes to UN tomorrow....Parole.