When a car is jump started.

Wired in parallel, not series

Automotive electrical systems are 12V, not 24V (though big trucks use 24V). If you put 24V to a 12V system the car would catch fire 🥵
Picture is 1000 words:

Sure there is. But it would take a lot of work. Lot more than hooking up cables
I don't think it takes that much work. You disconnect the negative cable on the car that gets 24 volts. Connect the negative jumper cable to the post and then connect that to the positive cable of the other car. From the other car connect the jumper cable to the negative post. Connect that end to the cable you just disconnected. Not that much work. But more work than a regular jump.
It is easy to get 24V when jumping a car, just connect positive to negative with one of your leads. And if you're feeling especially smart finish the other connection with negative to positive so your battery and jumper cables promptly explode/burst into flames 😧