The external strobes fire when their light sensor detects a light pulse above certain strength and duration. Typically this is produced by the camera's built-in/pop-up/clip-on flash. For cameras with a hot shoe, you can get an LED-based trigger which brings certain advantages - less drain on the camera's battery, fast recycle, support for additional modes, etc. For cameras without a built-in flash, such as Sony A6600 and A1/A7/A9 series, this is the only option when you're using fiber optics triggering. I use an A6300 in a SeaFrogs Salted Line housing with UW-Technics trigger and Retra Pro strobes; this combination allows me to fire strobes on half power at up to 3fps as well as use high-speed sync, enabling shutter speeds all the way to 1/4000s. In your case, you just need to pop up the flash and your YS-01s should fire, although you will be limited to approximately 1 shot per second and 1/160s shutter speed.
Keep in mind that the pop-up flash on the A6300 always fires in TTL mode (pre-flash which is used to measure needed strobe power, then main flash), therefore, if you want to use your YS-01s in manual mode, you need to set the mode knob to double lightning bolt setting - this will make them ignore the first flash pulse and fire on the second. Alternatively, you can put the strobes in TTL mode and use that - if you do, I suggest using center point metering and pointing the camera at the spot that you want illuminated, as otherwise the exposure tends to go all over the place.
