The mood of a tense indicates whether it expresses a fact, a command, a wish, an assumption, an obligation, etc. For example, the verb "to resign" is in:

Modern Persian has three moods: indicative, subjunctive and imperative. The optative mood is obsolete and is only found in some fixed expressions.

Indicative mood

The indicative mood is used to express factual statements.

باران نمی‌آید
Bârân nemiâyad
It is not raining
در خانه ماند
Dar khâne mând
He/She stayed at home
تهران پایتخت ایران است
Tehrân pâytakht-e Irân ast
Tehran is the capital of Iran
سفر چقدر طول می‌کشد؟
Safar cheghadr tul mikeshad?
How long will the journey take?

Subjunctive mood

As opposed to the indicative mood, the subjunctive mood is about non-factual statements. It is used to express possibility, uncertainty, obligation, desire, etc. In English, the subjunctive survives only in very limited situations e.g. "We insist that he do the job properly", "God save the Queen".

فکر کنم باران بیاید
Fekr konam bârân biyâyad
I think it is going to rain
بهتر است در خانه بمانی
Behtar ast dar khâne bemâni
It is better that you stay at home
شک دارم که بخواهد مرا ببیند
Shak dâram bekhwâhad ma'râ bebinad
I doubt that she wants to see me
می‌خواهیم شاد باشیم
Mikhâhim shâd bâshim
We want to be happy

Imperative mood

The imperative mood expresses direct commands or requests.

در خانه بمان
Dar khâne bemân
Stay at home!
ناراحت نباش
Nârâhat nabâsh
Don't be sad!