So you can present your ideas accurately and clearly
They are called a literary letter or a epistle
Short Summary: Richard (Gloucester) informs the audience of his emotional state and his plan to take over the throne.
Long Summary:
Richard III, at this point just the Duke of Gloucester, comes out to give the audience some insight into his state of mind and also the actions that have been happening before the play started. Even though the kingdom is in a state of peace, Richard isn't happy about it. He shares with the audience his plan to dethrone his brother (Edward IV), the current king, so that he can become king himself. The first thing he plans is to use rumors to make Edward (who is ill) suspicious of Clarence, their other brother.
Clarence enters, surrounded by guards because Richard's rumors have started to take hold, to be escorted to the Tower of London to be imprisoned. Richard uses this conversation to pretend he feels bad for Clarence and suggest that the rumors were started by Edward's wife Elizabeth or his mistress Lady Shore. He says to Clarence that he is going to try to get him free, but then when Clarence leaves he says to the audience that he is so happy to see him in prison.
Lord Hastings is the next to enter, just recently freed from the Tower. Richard informs him that Edward is sick and when Hastings leaves Richard tells the audience how happy he is about Edward's illness. He needs Clarence to die first so that he becomes the legal heir, then when Edward dies he will take the throne. Additionally, Richard wants to convince Lady Anne to marry him. His family was responsible for killing her previous husband (Henry VI, the former king), but Richard is excited to get her to marry him anyway.
