Hello, is it possible to receive a study guide of "The Lemon Orchard" by Alex La Guma? Please include the themes, an analysis of the characters, and important passages. Thanks.

"The Lemon Orchard" is a story that appeared in A Walk in the Night and Other Stories (1962), the first book by the South African writer Alex La Guma.
I will address the three sections of your question below. There is one important bit of background to understand: La Guma, born in Cape Town, came of age during apartheid. He was active in the resistance and in the non-white liberation movement. He organized strikes, supported key politicians, and wrote for a progressive newspaper.
"The Lemon Orchard" is set in South Africa in 1962, the same year it was published.
Characters
The story features a small group of men—all white—and one black man in a lemon orchard in the middle of the night. None are named.
The black man, a teacher, has apparently committed a crime: he had a disagreement with a (white) church minister. The white men bind his hands and lead him, at gunpoint, through the orchard. Despite the fact that their treatment seems unfair and cruel, the black man remains proud and dignified.
The white men, on the other hand, are not policemen. They seem to be self-appointed enforcers of the law bent on asserting their superiority over the black man. Their threatening behavior is not based on what actually happened with the church minister: they seem to hate the black man simply because he is black. The fact that he is black and educated only makes matters worse.
There is not a lot of specific characterization here, except that the four white men take some enjoyment in torturing the black man. The leader of the four men seems to be particularly cruel. "His eyes were hard and blue like two frozen lakes," La Guma writes, suggesting that he is merciless.
Themes
One of the clear themes in the story is the injustice of racial discrimination. The black man does not deserve to be threatened in the middle of the night. It is a reflection of the apartheid era, when black people did not have the same rights as their white neighbors.
Another theme is the significance (or insignificance) of outward appearance. In the story, the white men have an advantage over the black man simply because of their skin color. The fact that they take him to a lemon orchard—a place where the fruit looks beautiful and the air smells fragrant, though the citrus itself is sharply sour—reinforces the idea that there can be a great discrepancy between appearance and the interior.
Important passages

The bound man felt the hard round metal of the gun muzzle through the loose raincoat and clenched his teeth. He was cold and tried to prevent himself from shivering in case it should be mistaken for cowardice. He heard the small metallic noise as the man with the gun thumbed back the hammer of the shotgun. In spite of the cold, little drops of sweat began to form on his upper lip under the overnight stubble.

Here, we see the black man's pride even under incredible duress. Even though he might be putting himself in further peril, he refuses to let the white men see his vulnerability.

"For God's sake, don't shoot him," the man with the light said, laughing a little nervously. "We don't want to be involved in any murder."
"What are you saying, man?" the leader asked. Now with the beam of the battery-lamp on his face the shadows in it were washed away to reveal the mass of tiny wrinkled and deep creases which covered the red-clay complexion of his face like the myriad lines which indicate rivers, streams, roads and railways on a map. They wound around the ridges of his chin and climbed the sharp range of his nose and the peaks of his chin and cheekbones, and his eyes were hard and blue like two frozen lakes.

In this passage, we see how dominant the white leader is: even one of the other white men is nervous that the leader will shoot the black man for no reason.
Tthis excerpt also offers a memorable physical description of the details of the white leader's face. La Guma compares his face to topography.
They walked a little way further in the moonlight and the man with the lantern said,

"This is as good a place as any, Gom."
They had come into a wide gap in the orchard, a small amphitheatre surrounded by fragrant growth, and they all stopped within it. The moonlight clung for a while to the leaves and the angled branches, so that along their tips and edges the moisture gleamed with the quivering shine of scattered quicksilver.

This is the last passage of the story. It is haunting because we do not know what happens: do the white men kill the black man? This is "as good a place as any" for what? The horror of the possibility stands in sharp contrast to the lush natural setting where they are standing. It is an intriguing way to end this powerful short story.