What is the difference between the forms of LINQ research?

Question

What’s the difference between:

var query =  from s in db.DetailsRaWeb
             where s.cod_cli.Equals(Cod_Cli) && s.tag.Equals(TAG)
             select s;

and this:

query = query.Where(s => s.cod_cli.Equals(Cod_Cli) && s.tag.Equals(TAG));

As I understand it, the first performs the query itself, and the second filters the query?