If you don't get a ton of mail, just typing in the words you're looking for usually does the trick. I can just type lisa in the search box and get all of the messages from my friend Lisa, southwest to bring up my ticket confirmations, or "bank statement" to help get my finances in order.
But the real power of Gmail search lies in search operators -- words that help modify your queries. Search operators work pretty much the same way within Gmail as they do for Google. So, if I want the email Lisa sent me with her flight information so I know when to pick her up at the airport, I type from:lisa SFO. Likewise:
A link from my co-worker Michael: from:michael http
A photo from my mom: from:mom has:attachment
That last chat I had with one of the Gmail product managers: keith is:chat
All messages from ebay that aren't outbid notices: ebay -outbid (the hyphen tells Gmail to return all of the messages that don't contain the word that follows it)
The messages in my inbox sent directly to me that I haven't read yet: to:me is:unread in:inbox
You can limit the scope of your search to a particular subject (subject:) or label (label:) as well. And you can get pretty fancy. Recently, I was trying to remember the date of my friend's April birthday. I always send her a birthday email, so I searched to:maya (birthday OR bday) after:2007/4/1 before:2007/5/1. It's the 19th.
Extracted from: How to find any email with Gmail search, posted by Arielle Reinstein, Product Marketing Manager, Tuesday, May 06, 2008 8:28 AM