"Please pass forward your homework" is a command. Commands are written in the imperative form. The subject of the verb is implied and not directly stated in the imperative form. We know that the teacher is talking to the students when she says to pass forward the homework, but it doesn't actually say students.
"Today we will discuss poetry" is a statement of fact even though it takes place in the future. Statements of fact are written in the indicative mood.
"But today was the last day of the semester" is also a statement of fact. The sentence before this is written in subjunctive, but since this is not connected with punctuation to that sentence the verb is written in the indicative mood.
