There are two ways to search Gmail for emails, messages and attachments. You could either click on the down arrow available in your search box or you can use Gmail Advanced search using Search Operators. Search Operators in Gmail are words or symbols that perform specific functions. There are many examples and here are a few -- if you want to search for emails with attachments the search operator would be -- has:attachment. You can also specify file type like .Doc or .XL. There are a whole list of search operators available to use. Another example is if you want to search for emails larger than 5MB, you would need to use size:5M -- if you want to search for email that is older than a year the search operator would be older_than:1Y.

Advanced search operators are words or symbols to be typed into the search box in Gmail. Please find a few more examples in the video below.
Here is the link to get the complete list of advanced search operators for Gmail.

http://youtu.be/yzUWkgFTiro