Mail Questions

I'm using mail with gmail. I've created a smart mailbox, but it displays most emails twice; one from my inbox, and one from my gmail "all mail folder".

How do I get the folder to just display the email once?

What exactly is the difference between my inbox, and my gmail folders?

What is the best way to manage mail? I never use the Gmail folders, should I just archive them. Is there a good manual or setup documentation? I haven't found the stuff on apple's site very helpful.

I have gmail coming into my Mail on my Mac too but I don't have smart mailboxes as that's how I ended up with two emails.

Once you have created your gmail account, it should show up under Mailboxes/Inbox/gmail account (whatever the account is called will show) this is where your gmails will arrive.

Your Inbox should have mail arriving from your main email account.

Example
MAILBOXES
Inbox
Your main email account folder
Your gmail account folder

Under ON MY MAC, you can create folders and redirect emails to those folders if you want. To do that you need to Apply Rule to certian emails, so they move directly to the folders.