I'll see if I can cobble together an explanation of the functional differences that makes sense. An analogy -- Imagine a classroom full of students, with their desks arranged in the usual grid of rows, if I may...
Mechanical Shutter: The shutter (blinds covering the large window in the front of the classroom) opens, and the students are exposed to light. Each student scribbles down on a little notepad what he or she sees in their little corner of the window (top left student draws the top left area of the window, etc) until the shutter closes -- if the blinds were open too long, it's mostly blown out white. If it wasn't long enough, it's dark. But ALL the students were looking at the same time, for the same amount of time. The camera's processor (the teacher) then goes around collecting the notepads, and assembles the data they drew of the different areas outside into a single big photo. Film works this way, except there's no need for a teacher, the little notepads are all side-by-side and they physically make the negative. If the subject moved too much while the blinds were open, they notepads will show a blurry subject. Good? Good.
Electronic Shutter: There is no set of blinds on the window, it's just open. Each student has one of the eye masks on that you wear to try to get 4 hours of shitty sleep on a plane, so they can't see anything yet. But the window is wide open, they just can't see it. The exposure is going to be set for, let's say, 1/100 of a second, and there are (let's say) 100 students total in this classroom desk grid. They're going to look sequentially this time, not all at the same time, so that means each student gets to see out the window for 1/10,000 of a second... one hundred of those little increments will add back up to 1/100 of a second. Now, sequentially, the teacher walks around to each student, starting at the top left corner, working across each row and then back around to the left edge of the next row, on down and down to the bottom right corner, like eating an ear of corn, or like the old cathode ray tube tvs worked. Like typing a letter.... top left to bottom right, in rows. She removes the eye mask from the first student, top left corner. He/she's got 1/10,000 of a second to peek (they're fast at drawing, don't worry) and scribble on their pads what they saw in their little part of the window. Eye mask back down, then it's the next student's turn, etc etc. The teacher walks down each row, one at a time, letting each student peek out the window and draw it. The very last student, whose time slot is the last 1/10,000th of the total 1/100th of a second, draws what they saw, and that's it, the exposure is over. The teacher cobbles their drawings and that's your jpg.
Now, imagine that what's out the classroom window is a race car going by at ~180mph, from the left to the right.
Mechanical Shutter Class: Blinds go up, students ALL begin scribbling down what happens during 1/100th of a second ("that's way too slow to stop a race car's motion, what are you thinking?" I know...). When the teacher assembles all their drawing back into one big picture, it's a laterally blurry race car going past. The background is crisp, the car is evenly blurry across the range of where it was when the blinds first opened, to where it was when the blinds closed.
Electronic Shutter Class: First student's eye mask is lifted. Car is at the left edge of the window, so that student's little drawing of that corner shows the nose of the car just entering the scene, and it's crisp, not blurry, because this time the student only had 1/10,000th of a second to scribble. Next student's eye mask goes up, they begin to draw, but the car has moved ever so slightly to the right... 1/10,000th of a second has passed! Now keep going down the row of students til you get to the end. Next row, student's eye mask comes up and they draw. It's been ten time slots since the car started entering the frame, so now the car is even farther to the right. It's been one tenth of the total time! So the students drawing the next lowest row, their little slice of the car will be drawn farther to the right than the students in the row above them. Third row is even worse. Fourth row, worse. By the time you get to the tenth row, the car is now WAY farther to the right. But each student's drawing of their slice is crisp and stopped. The result is like those pics Bill posted here of race cars tilted at crazy angles... instead of a blurry car moving across the image, you have a crisp car tilted at an impossible angle.