In one sentence, describe what the following article is about:

It should be located in the upper right corner of the mail window. You will see that even as you start to type your search word(s), Mail begins to make suggestions. In this example, the search is for an email from a friend named "Colin" containing some password details. " When the search facility finds something relevant to the message you are looking for, click on the suggestion to set it as your first "search token." You'll see that as soon as you click on the desired name (in this case, Colin), Mail will show all mail received from him across all mailboxes. " When a search token has been set, it appears as a blue icon. If you wish to change the terms of the "search token," click on it to display a drop-down menu. In this example, you can see that the search token is set to find messages "From" the "Colin" chosen from the original list. By using the drop-down menu, you could also select:  "To" - to search for messages sent "to" the person selected from the list. "Entire Message" - to list all messages containing the word selected (in this case, "Colin." Click search box again and type in another search term. This can be anything from a word in the subject line to the address that the email was sent to. In the example, you are searching for an email containing some password details, so the word "password" is typed into the box. As before, you can change the terms of the search token using the drop down menu.

Summary:
Open the Mail application by clicking on its dock icon. Click on the search bar. Type a key piece of information relating to the message you are searching for. Assign your first "search token. Decide on the terms of the "search token. Narrow your search down. Click on the most relevant entry on the search results to set this as your next search token. Continue to enter additional search terms in the box to narrow down your search still further, until the message(s) you require become visible in the mail window.