Become confused about how Plex streams?

I’ve got an iMac running PMS in the same room as a Samsung tv using the Samsung Plex App and the router is also in the same room. Can I connect the iMac and tv to the router using ethernet cable instead of wireless ? Presumably in other parts of the house where I use an iPad I just get the relevant app and connect wirelessly ? With another iMac in a different room do I just use Plex Media Player (via ethernet) ?
Thanks for any clarification.

Yes. Generally ethernet cables will be faster than wireless which can help if you are playing high bitrate media.

I am guessing you have a router that does both wireless and wired. Things connected to that router either way are considered to be on the same Local Area Network (LAN)

Thanks that answers the question.