with your ROKU remote go to their streaming channels app store, or go to your ROKU account via computer/Iphone. At their app ‘store’ add your request for subscription to the Pluto app
As to traveling to other sites via URLs - we’ve a Samsung smart TV able to do that. DH has, from time to time used his phone to find the site and flung it to the TV for viewing.
Should Rumble and other video sites change the norm from You Tube...cringe at the thought as You Tube is (at this time) the only video site being offered.
I have the pluto app on roku. It opens to a crummy kid cartoon