The first ghost represents the past, and flickers in and out while glowing but is neither old nor young while neither male nor female.
When Jacob Marley comes to visit his old partner, he tells him he will be visited by three ghosts on three nights. His word is true. Scrooge awakens to find a strange looking ghost in his house: the ghost of the past. The ghost is described as having bare skin, with bare feet and arms. He or she is neither old nor young, and dressed in white. The contradictions continue in the fact that he or she has both winter holly and spring flowers.
But the strangest thing about it was, that from the crown of its head there sprung a bright clear jet of light, by which all this was visible; and which was doubtless the occasion of its using, in its duller moments, a great extinguisher for a cap .... (Ch. 2)
The ghost is kind most of the time, explaining to Scrooge that he is going to show Scrooge the past, but not just any past—Scrooge’s past. The past that The Ghost of Christmas Past shows Scrooge begins with his childhood and progresses to the more recent past. Some of the visions are hard for Scrooge to see. Sometimes the ghost goads Scrooge, but almost mostly gently.
He felt the Spirit's glance, and stopped.
“What is the matter?” asked the Ghost.
“Nothing particular,” said Scrooge.
“Something, I think?” the Ghost insisted. (Ch. 2)
The ghost seems to be able to see into Scrooge’s thoughts, and know when he is feeling something. He watches him, and leverages those emotions into helping Scrooge see how he affects the people in his life. These feelings are crucial to Scrooge’s development into a better person, and the other ghosts will use them to continue his growth.
At the end of the chapter, Scrooge finally can't take it anymore. He has seen Belle leave him, and then seen her with her family. He extinguishes the ghost because he can't take the idea that he could have had a family, when he ended up alone instead. Scrooge is finally realizing that all of the money in the world means nothing if you have no one to share it with.