All of your devices need a folder where you'd store data, those devices need to run a process called chunkserver (mfschunkserver) and simply add their storage space to the pool.
Mounting the pool is done using mfsmount (uses FUSE).
You'd need one of the devices (or another dedicated computer) to be the master (mfsmaster) that needs to be always online.
The restrictions are that all the machines must see each other over the network - either local lan or routed network (or a vpn where you set up routes).
Moose uses concept of goal and storage classes, you can simply set your files or folders to say goal of 3 and it will attempt to store 3 copies across however many devices (minimum 3 to meet this goal).
Storage classes are more complex and allow you to specifically control on WHICH chunkservers to store certain files/folders.
I'm using it across 4 machines, where 1 server is physically in Italy (Milan), another in Los Angeles (in a datacenter) and two more at home (also L.A.). One of my servers at home has 4TB drive so this one always stores everything, plus 2 copies across remaining 3 servers for redundancy.
All I need to do to have my data available to me is to VPN in to my network and run mfsmount on my laptop.