Clicking on the Gmail button activates the Gmail window. You can select specific labels, to transfer all of the messages contained within those labels, or transfer all messages to your iPod. You can also restrict messages to only those that are unread. The messages appear as Note entries within Gmail. Within the Mail folder the messages will be organized by label. iPDA uses Gmail's IMAP interface to extract messages so please ensure that you have IMAP support enabled within your Gmail account.
Note that to access Gmail iPDA needs your Gmail account name and password. The password is securely stored in your Keychain and you need to verify that you entered the correct password (via the Verify button) before iPDA can transfer your messages to your iPod.