Thats a male XT90 connector on your VESC, and male 4mm bullets on your motors. You are going to have to solder female 4mm bullets on to your VESC.
Since you have 3S batteries, I’m assuming you want to combine them to make a single 6S battery. To do this you need to connect them in series. You can either make your own series harness, or buy a connector from hobbyking.
Then you are going to have to cut the connectors off your batteries, and solder on male XT90s.
Plug the adapter into the VESC, then plug the batteries into the adapter, then plug the 4mm bullets into each other and your circuit should be good to go.
However, this has nothing to stop the spark from occuring when you connect the circuit. You may want to buy some sort of antispark switch or make a loop key.