See complete configuration on the wiki.
To let strype read your audio output you have to set up a loopback interface in alsa.
This is done by enabling the aloop-module in alsa and then telling mopidy to route audio to both your output and your loopback-interface.
Enable loopback interface.
modprobe snd-aloop
Tell mopidy to send audio to output (hw:0,0) and loopback (hw:1,0)
[audio]
mixer = alsamixer
output = tee name=t ! queue ! audioresample ! alsasink device="hw:0,0" t. ! queue ! audioresample ! alsasink device="hw:1,0"