Mood shows the kind of action.

Indicative mood: the declarative mood or mood of certainty. This is a statement of fact which assumes reality from the speaker’s point of view. This mood simply states a thing as being a fact.

Examples:

Bible study has changed Tim’s life. 

"He is thrown away as a branch and dries up; and they gather them, and cast them into the fire and they are burned" (John 15:6). 

Imperative mood: usually a command or entreaty. It is the mood of volition or will. The imperative mood in the Greek makes a demand on the will of the reader to obey the command; it is used to indicate prohibition and authority.

Examples:

Tim, study your homework.

"Abide in Me" (John 15:4).

"Ask whatever you wish" (John 15:7).

"Abide in My love" (John 15:9).

"Remember the word that I said to you" (John 15:20).

One aspect which will help your study of God’s Word is the understanding of the combination of the present tense and the imperative mood that is stating a negative command (a prohibition). The present imperative prohibition demands cessation of some act already in progress.

Example: 

"Jesus said to her, “Stop clinging to Me" (John 20:17). In other words, Mary was already clinging to Jesus, and Jesus was telling her to stop clinging and to go on refusing to cling to Him. 

Subjunctive mood: the mood of probability. This implies some doubt regarding the reality of the action from the speaker’s point of view. It expresses an uncertainty or an action which may or should happen. This is the mood used for conditional clauses, strong suggestions, or "polite" commands.

Examples: 

Tim may have done his homework. (Tim, if you do not do your homework, you cannot participate in the class discussion.) 

"That it may bear more fruit" (John 15:2). 

"As the branch cannot bear fruit of itself unless it abides in the vine, so neither can you unless you abide in Me" (John 15:4b).         

"If anyone does not abide in Me" (John 15:6). 

"If you abide in Me, and My words abide in you" (John 15:7).

Something else which may help you in your study of God’s Word is an understanding of the combination of the aorist tense and the subjunctive mood that is stating a negative command (a prohibition). The aorist subjunctive prohibition is a warning or an exhortation against doing a thing not yet begun.

Example: 

"Peter said to Him, “never shall You wash my feet!" (John 18:8a). In other words, Peter was telling Jesus that He was not to wash his feet and Jesus was not even to start washing his feet.  

Optative mood: the mood of possibility. This mood presents no definite anticipation of realization but merely presents the action as conceivable from the speaker’s point of view. (Used less frequently than the other moods.)

Examples: 

I wish my neighbor Tim would take The Berean Approach when studying the Bible. 

"May the Lord direct your hearts into the love of God and into the patience of Christ" (2 Thessalonians 3:5).

Mood	Relation to Reality	Usage of Meaning	Example
Indictative	Mood of certainty (reality)	Used to delare a statement of fact as something which is true. Expreses that which is actual, factual, or real from the speaker's point of view.	Bible study has chaned Tim's life.
Imperative	Mood of volition or will (potentially reality)	Usually used to express a comand or entreaty. Denotes intention, authority, permission, or prohibition.	Tim, study your homework.
Subjective	Mood of probability (probable reality)	Used to express an action which may or should happen but which is not necessarily true at the present, from the speaker's point of view. Expresses conditional or uncertain action.	Tim may have done his homework.
Optative	Mood of possbility (possible reality)	Merely presents an action as conceivable from the speaker's point of view, with no definite anticipation of realization.	I wish my neighbor, Tim, would take the The Berean Approach Bible Studies.