why show me maximum number of free account used in this device

Apple limits all iDevices to a max number of 3 total iCloud accounts. These accounts are tied to your devices hardware, so you could create a new account on a device that has not reached the max limit yet, but keep in mind that you cannot create more than 3 accounts per device.

Sign into iCloud either using another device, as suggested above, or a computer. You should then be able to sign in.