Quote from textbook "The META element provides a place to put mta information that is not defined by the other HEAD Elements.This allows an author to more richly describe the document content for indexing and cataloguing ... "
an example is META Name= "Keywords" Content=" pets,dogs,cats,rocks,lizards,supplies"
In terms of html text they go after < HEAD > and before < Body >
Some search engines use them although there are other uses eg using redirect to automatically transfer to another page or web site many basic meta tags define the document by identifying the character set used the program used to create them etc.
some info re search engine placement can be found click here