Wired Ethernet

I have a Roku 3 and Sonos Connect that need to use the same wired connection, but don't know how to create these two - splitter? They are located on a boat dock and are connected to the main router via additional cable in the house.
Just buy a hub/switch. Lots of different choices.

Here is One
Sounds like you need a network switch. The Netgear mentioned above should work. I use a gigabit D-Link switch and it works great.