Q: What does the status change from "With editor" to "With managing editor" indicate?

The evaluation processes at journals usually take time. Therefore, it is very important for you to have patience. I can understand that it is natural to be anxious about your manuscript, but you have just submitted it. It's too soon to be worried about the status changes. Don't keep checking your manuscript status obsessively, else you will find it difficult to wait through the weeks or months leading up to the decision. 

To answer your question, once a manuscript is submitted to a journal, it goes to an editor who assigns it to the managing editor for that particular subject area. The managing editor will then go through your paper and assign it to an Associate Editor(AE) who will be in charge of your manuscript till the final decision.

Related reading:

• What does the "With Editor" status mean for Elsevier journals?
• Is it too early to contact the journal?