@5js
Hi, to continue on . . .
You first need to install the Plex server program on your PC which you obtain from
www.plex.tv/ site, unless you have a better and more appropriate device to install it on. (I say this because I do not have it installed on a PC, I have it installed on my Western Digital WD MyCloud DL2100 NAS. It was designed to handle the speed, computing horsepower, and storage capacity necessary for optimal operation. Nevertheless, many people have it installed on their PC. Plex is a Media Server in the way My Media is, but more robust.
I have LOTS of ways to stream media files within my home as well as remotely. All the ways are useful depending upon the features they have. Plex has some unique features and I use it for that, but it is not my favorite way to stream. One uniqueness is the ability to stream music and video to Roku and Fire TV, tablets phones; even without also using Alexa voice commands and the addition of Alexa makes it even more useful.
So you will also need to install Plex channel on your Roku and after this all done you can stream media to Roku without needing Alexa. And, to add Alexa to the mix you need to install the Plex SKILL in your Alexa app. Before you incorporate Alexa into the fray, be sure that Plex and Roku play together as they should, Then add Alexa to the gang.
To use with Plexa, ask a nearby Alexa device the following kinds of questions and statements:
Alexa, ask Plex to tell me my devices (one you should here is name of your Roku; mine is named Family Room Roku.)
Alexa, ask Plex to set {Family Room} Roku as my preferred player).
Now you are ready to demonstrate and enjoy the power of this setup by saying something like,
Alexa, ask Plex to play (or shuffle) Dave Brubeck (any artist) to Roku. and if you have more albums than one they all will be shuffled up to around 20 tracks.
I do not have to specify Family Room, just say Roku, but we HAVE to specify the player otherwise it will play on Dot and not to Roku.
Use Roku remote to navigate using buttons at screen bottom.
Another example, right now I have Plexa playing artist Ken Emerson on Roku (I have four albums) and they are being shuffled and played. I said,
Alexa, ask Plex to play Ken Emerson on Roku....... and Plexa did the rest, including shuffle the albums and tracks to Roku and onto TV and stereo in glorious sound quality.
That's it, so get it all up and running and be sure to use the Roku buttons to see what each can do; last button shows the list of what is playing. Cool.
Once you have the music mastered, ask me how to play videos, movies and I can explain that.
BTW, all the music on my server is from a COPY of my iTunes Media database on PC and movies on my server are mp4/m4v files I made from DVDs with free Handbrake program.
HAVE FUN with this!