Looking at the sun without special glasses or even a welding helmet can damage your eyes and cause blindness.
The intense visible light rays from the sun can penetrate your eyes and damage the retinal tissue which can lead to poor eyesight or even in some cases complete blindness.
Although it's very hard to look directly at the sun even for a few seconds because I tried that when I was a kid and I immediately looked away from the sun because sun was too intense.
I had poor vision for half the day after that but then my eyesight cleared back up.
If you want to stare at the sun you can put on a welding helmet which blocks the UV rays from the sun so it doesn't burn your eyes.