It depends on your mail account's protocol. If it is IMAP or Exchange, then yes. Create new folders (on the server, not your computer) using the website or a computer client. They will automatically sync on the iPad.
If your account is POP, then you can not. POP does not support syncing of folders. Many email providers support both POP and IMAP, so if you can't sync folders now check with them to see if they have the other option.