Thanks for confirming the version.

I think the volume adjust works a bit differently on Sailfish compared to Android.
In Android you can change the level of ringtone, media, alarm, ...etc side by side.
In Sailfish, how I experienced, I need to use one of those functions to be able to change the correspondent volume.
Example: when I don't play video and am not in a phone call, if I press the volume rocker it changes the ringtone volume.
If I am playing a video or mp3 and I hit the rocker, it changes the media volume, but only when I am doing some media playing.
If I am in a phone call, it changes the speaker volume.
Maybe there is a way to change these when I am not in that 'action', but I don't know how.

I just have installed Talefish and played some mp3. It works fine. I can stop, play, go forward/backward without any issues. Are you sure that the playing has not started just the volume is down? When you start the mp3 play, please hit the volume up rocker a few times.

Do not worry about being new, it just means you can learn a lot (if you are willing to learn of course). I have met with Sailfish only a few months ago too.

Ironically I purchased my Nexus 5 because I wanted to try Ubuntu Touch. Then I found Sailfish and thought would give it a go. After a few days use of UT, it was a big disappointment and almost instantly I installed fell in love with Sailfish.
The guys at Jolla who developed this system are just simple amazing and I am very grateful they made it available for the public.