Everyone and their mother phrase informal
A large number of people
When I went to the cinema last night, everyone and their mother was there.
Everyone and their mother will come to my birthday party tomorrow.
A group of bad or sinful people
To count the number of people in a group to determine who is present
One needs to understand the basic techniques or primary details of something before taking actions that require greater skills
Peter failed because he did not learn to walk before he ran.