Select them all, click on play. In there is play and play all. This really isn't rocket science.
Open your file explorer, look for that symbol at the top right, click it and bingo bango...you now have the ribbon.
View attachment 25639
Now open you music folder, open the ribbon and you'll now see exactly the same thing in Trouble's attachment. Select your song(s) and then select play all....
At the top in the Ribbon under "Play". See attachment.
I suppose it is possible that if you are using some third party overlay that provides some earlier version of a start button that perhaps it has also crippled other functionality within Windows 8.1 Pro as well.
You should have a Ribbon in File Explorer and if you don't then something is wrong.
I suggested Google, not to be patronizing but because there are any number of ways that the Ribbon can be disabled