Depends on the semantics of "blind". The eye doesn't just completely turn off, but it will have severely decreased vision, and the person may only perceive stuff with it when the good eye is closed.

Brain science is still new and not fully understood, but there are groups of neurons in the brain called ocular dominance columns that light up when one eye or the other is stimulated. In most people there are equal numbers of ocular columns for each eye. But in brains that had a bad eye during infancy, most of the ocular columns will be linked to the good eye. In other words, the brain literally rewires itself to be essentially one-eyed.

Yes. Normally, your brain takes two separate but similar images from your two eyes and fuses them together to make your "vision". When the two images aren't similar however, like if the picture from one eye is much blurrier or you have a lazy eye that's pointing in a different direction, they're too different for your brain to fuse together. Instead of confusing you with two dissimilar overlapping pictures, your brain says "well, this is probably the right one and it'll be good enough" about the good eye and literally just stops displaying the bad eye to you.

After a while, it stops even checking to see if the bad eye has something useful to display since it never ends up using it, and the pathway from that eyeball to your brain atrophies. All brains are plastic, meaning they can create new pathways, but babies brains are way more plastic than adults, so it's critical to correct this issue as soon as possible. You can try to fix it when someone's older, but you're unlikely to be as successful.

If you don't fix it in time, the person will literally stop being able to see out of that eye because the path that sends the image from the eye to the brain just doesn't work anymore. Nothing happened to the eye itself, but without that connection the image won't get to your brain for you to be able to see it. You'll mostly see out of just one eye when you have both eyes open although if you close your good eye you may still be able to see something out of the bad eye depending on how atrophied that pathway between the eye and brain are. However, you'll probably never be able to completely successfully fuse two images together, which can result in lifelong vision problems.