The volume control is disabled by default. Open the web interface and go to "Settings" then "MPD". Here you will find a drop-down menu for "Mixer type". Change it to "Software". Now you should be able to change the volume.

Hope this helps.

Fellow Noobie here (and not many years younger). If it’s any consolation it took me a number of attempts to get things working even with the latest version of Raspyfi. It’s important to do things in stages & the first thing is to confirm you are at least getting some audio out of the Pi. The audio output selected by Raspyfi is set by default in this order:
1 USB DAC
2 HDMI
3 Analogue out via the 3.5mm outlet on the Pi
I’m assuming you haven’t attached your DAC yet. You have confirmed that Raspyfi boots successfully (the headphone logo), so you should disconnect the HDMI. That will ensure you should get audio out on the analogue outlet, when you power up the Pi.
Now you need to get some audio playing through Raspyfi.
Start simply with a USB stick with a few music tracks on it, not in folders, but at the top level. Make sure you update the MPD database. Select Browse / usb1 and the music tracks should be listed. On the right of each track select the action list icon and Add to the playlist. Select Playlist, select one of the tracks and play it. You can verify it’s playing in the playback window & all being well you can hear it. You are over the first hurdle.
(Perhaps surprisingly it was using the device as an Airplay receiver that I succeeded in confirming the audio was working. At least I didn’t need to update databases on USB or NAS devices to test that. If you have some music tracks on an iPhone (3GS or later) running iOS 5 (or maybe 4.2.1) or later it should be straightforward).

I found the Webradio less straightforward, but only because I kept choosing the first station on the list, which turned out to be not functioning, so I never heard any audio. Choose one of the Linn channels - those are reliable - add to the playlist and you should be over the next hurdle.
Next you want to try out your DAC. For me that was the start of weeks of frustration, hours and hours of scouring the web for a reason why it didn’t work (caused Raspyfi to freeze in fact). Today however I cracked it and I’ve been listening to audiophile quality via Raspyfi for hours. All I’ve got to sort out now is getting Raspyfi to recognise my NAS.

It’s well worth persevering. Let us know how it goes.