that esc needs a seperate bec, sorry if you already know this, but what that means is it needs a seperate power source to power the rx, and then the esc, so plug it into channel 2 (throttle) and you need 4 x aa batteries (6v is a safe working voltage) into the rx in "batt" slot. Always ensure the voltage is good, dont leave connected, if it drains away whilst in use you could lose the signal and your boat will become uncontrollable
a cheap voltabe guage plugged into AUX in the rx will be a visula monitor of rx battery supply condition.
The seasprint also needs 6 cells minimum, I used it a lot some time ago, its a good esc, not water proof though so stick it in a plastic box of some sort for extra protection