Grammatical mood

This term refers to verbs and the mood of the speaker/writer. Fortunately in English, it is a simple matter and one we do not have to worry about.
The imperative mood is that of commands: Go away!
The indicative mood is the normal one when we tell of what will happen, has happened or is happening: I shall go; I went; I am going. Note that it applies to any tense of the verb.
The subjunctive mood hardly exists in English but, if you learn French, you will have to master it as the mood of uncertainty and emotional input.

MOOD and TONE

In literary analysis it is helpful to acknowledge or create a distinction between these terms:
mood represents the writer's feelings towards his/her subject matter; tone results from her/his attitude to the topic.
The mood might be sad or joyful or any other emotional state whilst the tone could be ironic, adulatory etc and is more a mental state.