On your handlebars you'll find 2 sticky-out things, probably silver in colour. These are commonly referred to as brake levers. Pull them in an emergency and you'll stop.
Many e-bikes do have cut-outs integrated into the brake levers, and these are mandatory in Europe with their pedelec bikes. The controller has to have the facility to connect these though.
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It's a good idea to have a switch to isolate the battery which is independent of the controller. With a brushed controller failure, power can become permanently routed to the motor.
I had that happen to me on an old Powabyke! Going down a steep hill so didn't notice 'til I tried to slow down and stop at the bottom (the Powabyke didn't have brake lever motor cut outs....). The fun was brief, but the memory lingers on.....