vous can have two functions: to address more than one person, and as a polite form of address to one person when there is a certain 'social distance' between the speaker and the addressee.
tu is only used to address one person when there is no social distance between speaker and addressee.
In its plural use, vous refers simply to more than one addressee, whether social intimates or not.
When one person is being addressed it is difficult to give hard and fast rules about when to use tu and when to use the polite vous. Generally, one can say that the non-native speaker would be well advised to use vous from the outset, and to allow the native speaker to take the initiative to change to tu. It is not possible to give an exhaustive list of other such usage. Individual speakers may vary in their own preferences for use of tu or polite vous, and that usage may vary regionally (for example, it is often said that tu is used more readily in the south of France than it is in the north).
'Marked' use of tu
Certain social sub-groups have their own internal norms for the use of tu and polite vous. For example, in sports teams, in left-wing political parties, and in trade unions, tu is the generalized form of address.
There are also a number of contexts where the expected use of polite vous between speakers is not met, and the actual pronoun form used is tu. For example, a stranger approaching you in the street and using the tu form, where normally vous is expected, may create the impression of an unwanted degree of intimacy; or it may indicate arrogance or contempt.