Normally, nobody looks at the Sun except for brief glimpses. During the partial phases of an eclipse, the Sun is still much too bright to look at, but people tend to stare at it anyway. For the partial phases, you need a dark filter like a “solar viewer,” “eclipse glasses,” or a #14 welder’s glass.
Even when the Sun shrinks to a skinny crescent, the Sun is still too dazzlingly intense for direct viewing.
When the last bit of crescent vanishes, totality begins.
Only during totality, is it entirely safe to view the eclipsed Sun. You will see a dark circle surrounded by the Solar Corona, the Sun’s atmosphere.
The corona is no brighter than the Moon is at night. It’s safe to look freely and you can use binoculars or a telescope for a closer view. But remember: totality is short. You have only two minutes of totality.
When the crescent reappears, you must again view the Sun through dark filter glasses or viewers.