Have 3 external Drives how should I set up?

Portable Drives easystore Portable Storage
1

I have a MyCloud, Easystore portable and My Passport Wireless Pro.
I need to know in what order i should set these up. Since I don’t have enough storage on computer to store all my pics and documents, I need to use 1 as main storage drive to, then one of the drives for back up or sync and lastly extra just in case.
Any advice would be greatly appreciated.