[How to do instruction] Setting up Library

[DRONE7]

I really am a newbie and none of this makes any sense ! Somebody PLEASE walk me through the steps required to play music from a USB stick inserted in the pi. Thanks

Presumably you are at the moode web page using a browser on another device ?
With the USB stick connected to your Pi...

If so you will see top right an 'M' icon....click on that and a dropdown menu appears where you can find and click on 'Update Library'
While the update happens a small spinner appears top right.
Once that stops then click on the main 'artwork' image and you will be taken to the Library screen where you can select the items you wish to play.
This screen has a menu top left for viewing various ways...try 'album' or 'folder' views.
In album view each album cover has 3 dots within it. click to see options...at this stage use 'add/play'

Provided you have configured your audio device in the setup screen (Main menu-Configure-Audio) then you should have music.