Received: headers show the path that a message takes from the message sender to the final recipient. They are read in reverse order, so the Received: header at the top of the message is the one that delivered the message to you, and the last one shown should be the one where it left the sender.
Received headers must include at least one entry for every server that handled a message. However, spammers will also sometimes forge additional Received headers, before they send the message, to make it look like the message originated somewhere else.