Charge Butter Bot before you use it for the first time.
Butter Bot
Any standard USB-C charger will do — the same kind you already use for most phones and laptops. Just plug it in; there's no special adapter to hunt down.
The controller
The controller's batteries aren't rechargeable — but you can plug the controller into USB-C and run it straight from that instead, using the cable as its power source.
So it's the same USB-C cable whether you're topping up Butter Bot or powering the controller.
And yes, it's safe to leave it charging on the desk — Can I leave Butter Bot charging on my desk?
Not sure when it needs charging? See How do I know when my Butter Bot's battery is running low?