To Lolly and Mickey

In a post below, Mickey and Lolly, you both mentioned the lymph system. Can you explain
this and what you mean by the lymph location? Are we talking armpits, collarbones, up in the neck? Lolly, you mention supraclavicular lymph nodes and someone in this talk mentioned the neck. Can you both share the location of these lymph nodes of the neck? Are they by the collarbone or higher up on the sides? Do they biopsy a lymph node to see if it's cancerous or do some other test?

Thanks.