I submitted a paper to an Elsevier journal, but it was not assigned to a reference number. They sent me a mail stating that the paper with the managing editor for initial evaluation . After tow weeks later, I got mail stating that the paper is with the Editor. And it was assigned to a reference number. What does this mean? Thanks in advance.
"Managing editor" can mean many different things, e.g. for one of the journals I used to handle, the managing editors were effectively editor-in-chiefs using a different name.
In your case most probably the managing editor is some kind of gatekeeper to the journal. It could be the editor-in-chief, or it could be an employee of the publisher. They looked to see if your manuscript was within scope of the journal, and if it was, who the best member of the editorial board to handle it is. Then they forwarded the manuscript to that editorial board member.
There's nothing else to do except wait.