The device you need is called a network switch. It allows multiple network devices to be connected together to enable them to communicate between each other.
Typically switches are available with either 10/100 (fast Ethernet) or 10/100/1000 (Gigabit Ethernet) ports with the latter offering faster speeds although the faster speeds are only really of benefit if the port on the router that the switch s connected to is also a Gigabit port.
If the switch has an up-link port connect this to the router and then connect your devices to the other ports. If there is no up-link port then all the ports are equal so it doesn't matter what order the devices are connected to.