what is the use of 'los-' as a prefix?

attached to most verbs, the 'los-' prefix simply implies starting to do something. For example: 'sie fahren' = 'they are driving', and 'sie fahren los' = 'they are setting of (by car)'. Generally speaking 'los-' will be found with verbs of motion to imply some kind of setting off, but that is not a hard and fast rule and you can use it with other verbs too. The verb 'loslegen', for example, means to set about doing something, and can be used in relation to any action. for example 'Lass uns loslegen' = 'lets get down to business'. Unlike the other examples of how 'los' can be used, this particular verb 'loslegen' doesn't really bear much relation to its stem (legen = to lay).