Who are the characters and what events occur in Act 1 of Much Ado About Nothing?

In Act 1 of Much Ado About Nothing, Shakespeare begins setting up the two central conflicts.

The first conflict is between Prince Don Pedro and his illegitimate brother Don John. As an illegitimate brother, Don John is not entitled to the crown and is jealous of Don Pedro's position as ruler of Argon. Out of jealousy, Don John will do anything he can to overthrow his brother, even if all he can do is disgrace his brother by tricking his brother's dear friends.

A third major character Shakespeare uses to set up the first conflict is Claudio, a prized soldier and friend of Don Pedro who has just returned from the war. In the first act, Claudio falls in love with Hero, and Don Pedro promises to woo her for him since her father is already reserving her for Don Pedro. However, upon learning of their plans, Don John makes plans of his own to sabotage the courtship by making Claudio believe Don Pedro is wooing Hero for himself.

Two more characters Shakespeare uses to develop the second major conflict in the play are Beatrice, cousin of Hero, and Benedick, another prized soldier and friend of Don Pedro. Beatrice and Benedick secretly feel more affection for each other than either one cares to admit and hide their affection behind a war of wits. Benedick even declares he hates women and promises to be a bachelor all his life. Towards the end of the opening scene, Don Pedro promises that he'll see Benedick "look pale with love" (1.1.227), a promise that leads to trickery in the second act.