The best adult channel is SCORETV https://owner.roku.com/Add/SCORETV
Go to http://www.scoretv.tv/?roku=how
for more instructions on how to add our channel.
What you will need to do is log into your Roku account and add the private channel: SCORETV
Then from your Roku's Channel Store, select the SCOREtv channel and follow the instructions shown on the screen.
Here is a video to help you add a Private Channel to your Roku. http://www.youtube.com/watch?v=T3ArGH6QuWA
We also have a FREE channel at https://owner.roku.com/Add/SCORETV1
to get your mouth wet.