You can find your device MAC addresses on the bottom or back on your Roku player (depending upon model). A MAC address is a set of six 2-digit pairs separated by colons (e.g. 00:0D:0A:1H:3G:5C). One set is for your wireless connection and one set is for your wired/Ethernet connection, if your Roku player model supports Ethernet. 

Alternatively, from the Roku home screen, select Settings> About. The MAC addresses will be listed on-screen.