iCloud sync if no Wifi

I need a really dumbed down answer please.

I am currently syncing using iCloud. I am not using WIFI. I don't have WIFI. I want my phone contacts and calendar to be separate from my Macbook. I use iTunes to back up my apps. I'm using Leopard as my OS. I'm not a really sophisticated user and just need stuff saved if I lose my phone.

I keep getting a message that tells me I haven't backed up my phone in 3 days. I understand now I have to plug my phone in to my computer using a USB while it is locked and let it sync.

Is that all I need to do? As soon as I change a contact it gets backed up to my computer so I don't understand the message.

When I do look at my phone under Settings>iCloud>Storage and Backup> iCloud backup is on and where it says BACK UP NOW is grayed out. It also says I have never backed up. Huh?

I"m trying to avoid having stuff sync back to my phone from my computer and have a bunch of duplicate information I do not want.

So please keep it really simple. I just don't get this and just need the basics.

Thanks in advance.