Hosa CMP-303 Interconnect Cable - 3.5mm TS Male to 1/4-inch TS Male - 3 foot

Welcome to the synth world! Love the East Beast. You can plug 3.5mm headphones directly to the "Output" (top right of the interface). You can connect to an audio interface too. For that, you'll probably want a cable with 3.5mm on one end and 1/4 inch on the other end. I use these. The smaller end goes into the East Beast's "Output" and the bigger end goes into an audio interface.