One or two sentences is not very much space to thoroughly summarize the entire play of Macbeth. Therefore, you are going to have to be very general in your summary. It should be easy to focus on the character of Macbeth, as the plot centers on him. You will also want to mention the themes of fate, ambition, and guilt—which are very central to the story's plot.

Keeping all of this in mind, your summary could go something like this: Macbeth, an ambitious Scottish general, hears the prophecy of three witches that he will become king. Therefore, at the urging of his wife, he murders King Duncan and assumes the throne—only to be consumed with guilt and suspicion before being vanquished by his enemies.

To provide such a short summary is a difficult task so I will give you some ideas and you can select from those. Start with key words to help you make your selection such as

• the battle between good and evil  -  this encompasses the themes of appearance versus reality including the natural and the unnatural, loyalty and honor versus treachery and order versus disorder
• Macbeth - a noble warrior is reduced to an irrational "idiot" - to use his own words: "It is a tale Told by an idiot...Signifying nothing"
• The influence of others and acceptance of responsibility for one's own actions which bring a set of consequences.
• An unfailing belief in Macbeth's contribution to his own fate or destiny.

From the above, you could conclude that

Macbeth is about one man's failings and his complete self-absorption and failure to accept the consequences of his immoral and unthinkable acts. Who started out as a noble warrior and indeed a hero in his king's eyes becomes the epitome of evil in the face of an environment where "fair is foul and foul is fair. "