The official languages of Canada are explicitly mentioned in the establishment of the Canadian government and are English and French.
There are other official languages, such as the languages of First Nations peoples, but English and French are the primary ones and the ones used by the vast majority of Canadians.
English is spoken by most Canadians, but there are certain regions throughout the provinces who speak French more commonly. The province of Quebec exclusively speaks French and there English is considered the minority language.
People who wish to immigrate to Canada must learn to be somewhat functional in either French or English. Also, when Permanent Residents apply to become citizens they must be able to pass competency tests in one of the official languages. Most people are able to become familiar enough with the languages simply by living in Canada and using the language regularly.
English and French are the most widely spoken languages in Canada, but that isn’t the only reason for why they are the official languages.
When the Canadian Constitution was being drafted, politicians and legislators had to consider the existence of Quebec. The province of Quebec was, and still is, a sovereign region in Canada. It is much like its own country within a larger country. Recognizing this separateness was an important consideration to legislators.
The solution, which is called bi-culturalism in the Constitution, was to establish French as an official language as well as English. This was done to protect the sovereignty of French speaking residents and citizens of Canada.
More recently, it was decided that the spirit of this legislation was to support multiculturalism. Instead of supporting the independence of only two cultures, all cultures in Canada will be respected.