At first sight, he experiences pain and confusion, unable to see, his eyes blinded by the glimmer of the fire, his mind confused as he tries to make out the shapes over the wall, which appear less obvious than the shadows of his reality. He is then dragged up out of the cave and he is not able to see anything because of the sunlight. At first, he sees shadows but eventually as his eyes adjust to the daylight and he will see objects more clearly.
In the Allegory of the Cave, Socrates explains to the student how we are blinded by what we are only allowed to see (shadows in the cave). If we were to see the truth (sunlight outside of the cave), then we would tell others, but they would not believe you.
The world inside the cave is an analogy for the human mind, specifically education, even more specific, lack of education. The world outside and above the cave is the area where knowledge and reasoning is