Doesn't matter if it's a "smart tv" - you'll be connecting the Roku as an external device.
Yes, it will need an HDMI cable to connect it to an HDMI port on your tv.
Roku has had a number of different models under the Roku 2 name, some of them with letter designations (Roku 2 HD, Roku 2 XD, etc.) issued from 2011 to 2015. They are outmoded and painfully slow by today's standards, and many of the more recently developed channel apps won't run on them.
Roku Community Streaming Expert I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well. If this post solves your problem please help others find this answer by clicking " Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X