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.