HOw to use a jumpstarter?

Another reason to connect the black lead to the engine is because its connected electricly to the starter.
By doing that you bypass a possible electriclly sucking poorly connected negative cable from the flat battery.

But sparks is a good safe thing to do. Those battery's really do explode if things go wrong.

AND so totally agree's is the dude that DID have a battery explode in his face.
Earned a 1st time ever set of glass's for that.

45 years later had eye surgery for buggered eye muscles & still not fixed properly.

1: MAKE SURE NOTHING is switched on inside the car & doors/boot are closed. (ALL lights etc MUST be OFF)
2: Connect positive jumper lead to jumper battery
3: connect the jumper battery positive lead to the car battery positive terminal.
4: connect the negative lead to jumper battery
5: Connect jumper battery negative lead to a solid part of the engine block

6: Attempt to start the engine.

The accident was from testing a bare starter motor on a battery that a workmate had just taken off the charger (unknown to me)

make sure seat belt is on. when you drive away

The old advice of connecting "live" terminals first, then grounds last, comes from the days when cars had very rudimentary charging systems, and batteries commonly gassed hydrogen. By connecting grounds last, and some distance from the battery, you avoided the chance of a spark igniting the the hydrogen. And you also had less chance of "shorting" the last lead you connected out.

Advice about the best technique now has some differences of opinion.

Modern batteries with modern charging systems are much less likely to have gassed hydrogen, so its less of a risk.

But the electronics in the vehicle all rely on a good ground connection for their inbuilt protection to work properly.

And, if you are jumping the next generation of vehicles, some or all of those batteries may be up to 48, 72 or even higher voltages. Connecting the "live" side of the batteries first carries the risk that the car bodies may be left at different voltages, especially if one battery is heavily discharged.

24 volts on a damp day may make you jump, possibly into danger. 48 volts will make you jump, may even under some circumstances stop your heart. 72 volts almost certainly can stop your heart.

So I expect the "next generation" of vehicles to come with "don't jump start" labels, or a change to the instructions, to require earthing of vehicles first.

When connecting jumpers. as you put the last clamp on,always give it the "tap tap" test 1st. a shower of sparks tells you you've done something wrong.