What were the two major topics that Darcy unfold in his letter to Elizabeth?

Mr. Darcy gives Elizabeth his letter, then quickly leaves. First the letter explains Darcy's reasons for persuading Bingley not to marry Jane. Darcy admits that the impropriety of the Bennet family made him hope that the two would not marry, but that his main reason for preventing Bingley from proposing to Jane was that he did not think that Jane had any particular regard for Bingley. The only part of his conduct which he is uneasy about is that he concealed from Bingley his knowledge that Jane has been in London for the past few months.

In response to Elizabeth's charge that Darcy had injured Mr. Wickham, Darcy relates the whole account of Wickham's relationship with him and his family. Darcy's father was very fond of Wickham and paid to provide him with an excellent education. Before his death Darcy's father asked Darcy to promote Wickham's professional advancement and stipulated that if Wickham should become a clergyman Darcy should provide him with a good family living. Wickham, however, having no desire to become a clergyman, wrote to Darcy after his father's death and asked for money in order to study law. Darcy gave him 3,000 pounds and Wickham resigned his claim to assistance in a church career. However, Wickham quickly gave up on studying law and squandered the money with a dissipate lifestyle. When he needed more money he went to Darcy and told him that he would become a clergyman if Darcy would provide him with the living that had been promised. Darcy refused, and Wickham was furious. A while afterwards, Wickham, with the help of Miss Darcy's governess Miss Younge, managed to deceive Darcy's younger sister into consenting to elope with him when she was fifteen. Darcy happened to go see his sister before the intended elopement and she ended up confessing the whole plan to him. He thus prevented the elopement, the motives for which on Wickham's side were mostly Miss Darcy's fortune and a desire to revenge himself on Mr. Darcy.

-he was wrong about Jane not loving Bingley.

-He comes clean about what actually happened with Wickham.