According to Google
"Google Mail is a free, search-based webmail service that combines the best features of traditional email with Google's search technology. Google Mail makes locating messages so easy that you will never need to shuffle mail in your inbox again. Besides offering an entirely new way of reading and tracking messages, Google Mail includes more than 2,500 megabytes of storage space (over two gigabytes)."
Maximum attachment size : 20 MB
Key board shortcuts are available here...
Google Mail's rich formatting options when composing helps to forward the inline pictures.
Grouping all replies with their original message, creates a conversation.
The meaning of the icons used in google mail are available here...
Gmails doesnt have folders concept.. they use labels instead. For creating labels visit here.
Google mails languages are listed by google in its help.
You can get the mails transfered in to google mail(even from non google mail accounts) using mail fetcher.
Finally, if your mail is firstname.lastname@example.org, all the mail send to email@example.com, firstname.lastname@example.org etc... will all get delivered in to your account, google ignores the dot (".").
Google itself have said about the same in Am I receiving someone else's email?
For anything and everything you can visit help center.