how is he revealed at the begining of the novel

We might notice right away, in Hamlet's first soliloquy, how difficult he can be to follow – how much his speech jumps and roils around, allowing interjections, playing with allusions and puns, becoming frequently side-tracked by this or that image. This tendency of Hamlet’s, to become sidetracked by his own train of thoughts, is crucial to the play, and crucial to the central motivational mystery of Hamlet – the delay of the revenge. But we will see much more of that to come.

We might also note that in his first soliloquy Hamlet appears deeply “depressed,” as we would put it today, or “melancholic,” as the people of the early seventeenth century would have put it. The audience of Hamlet’s own day would have expected as much. The play belongs to a genre known as “revenge tragedy.” Such plays occupied many of the greatest playwrights of the generation directly preceding Shakespeare’s, including Thomas Kyd, but by the time Hamlet was written they had come to be seen as rather old-fashioned. Like any genre, revenge tragedy has certain predictable conventions, one of which is that the protagonist of the play is melancholic – dominated by saturnine, sluggish, pensive “humors,” or bodily spirits. In Hamlet, Shakespeare, rather than simply repeating this convention, explores it as a convention. That is, he gives us the archetypal revenge hero, the most introspective, most melancholic, most pensive hero ever seen on the English stage.

At the same time, Hamlet seems somewhat aware that he is, in fact, playing a role on stage. He notices his own costume and makeup (“’Tis not alone my inky cloak, good mother [...]” (I.ii.77 ff.)); he refers to specific areas in the theater (as when he notes that the ghost is “in the cellarage” (I.v.150)); in short, he seems at once to be the most typical of types, and to be an audience to his own typecasting – and furthermore, he seems to be distressed about being so typecast, and anxious to prove that there is something genuine behind his theatrical veneer. In general, critics have long noticed that Hamlet is a play about plays, most specifically a revenge tragedy about revenge tragedy, and the pretzel-like self-referentiality of the protagonist is the main reason why.