What language features does Shakespeare use to show us the relationship between Macbeth and Banquo in Act 3 of Macbeth?
I can't find any examples of language since I don't understand most of what I'm reading
The language in Macbeth and Banquo's conversations with each other and their soliloquies in Act 3 shows that each is beginning to be suspicious of the other.
When reading Shakespeare, it is best to look for the broader meaning and not try to understand it word for word. It is also helpful to read a summary of each Act beforehand, so you know basically what is going to happen. We also have translated versions of the entire play here at enotes. I have included a summary in the first link, a translated scene in the second, and an article on understanding Shakespeare's language in the third.
Macbeth and Banquo used to be friends. When they are talking together in Act 1 they are easy with each other, laughing and talking. However, by Act 3 the relationship has deteriorated into suspicion.
Each character has a soliloquy in Act 3 that shows he suspects the other. In the beginning of Act 3, Banquo is talking to himself alone about how he feels that Macbeth has stolen the throne by killing Duncan. He believes that Macbeth has played most foully for it (“Thou play'dst most foully for't”), or done terrible things to become king.
If there come truth from them—
As upon thee, Macbeth, their speeches shine—
Why, by the verities on thee made good,
May they not be my oracles as well
And set me up in hope? (Act 3, Scene 1)
Banquo is indicating Macbeth’s greatest fears that his sons, and not Macbeth’s, will be king after Macbeth, because the witches prophesized that too. Macbeth gets annoyed that he has a “fruitless crown” and this is one of the reasons he decides to kill Banquo (and his son) to prevent his sons from being king.
When Macbeth enters, Banquo immediately becomes subservient, telling him his “duties [to Macbeth]/Are with a most indissoluble tie/Forever knit. (Act 3, Scene 1). He is trying to make Macbeth think that he is not at all suspicious, and he is completely loyal to Macbeth.
Macbeth isn’t buying it. He says that his “fears in Banquo/Stick deep” because he knows too much and is a threat to Macbeth’s family line keeping the throne.
Macbeth is already planning Banquo’s murder when he asks him if he is going out riding. He will not kill Banquo himself. He hired three murderers to do it for him.
Macbeth can’t get the fact that Banquo knows about the witches and his sons are supposed to be king out of his mind. He does not rest after killing Banquo though, because he sees Banquo’s ghost sitting in his spot, the embodiment of his fears, at the banquet. Macbeth is so disturbed by the vision that the party has to be broken up early.