what is subjunctive mood? present, past and future?

The subjunctive is a special kind of present tense which has no -s in the third person singular. It is used in that-clauses in a formal style after words which express the idea that something is important or desirable (e.g. suggest, recommend, ask, insist, vital, essential, important, advice). The same forms are used in both present and past sentences.

e.g. It is essential that every child have the same educational opportunities.
We felt it was important that James write to uncle Arthur as soon as possible.
Our advice is that the company invest in new equipment.
The judge recommended that Simmons remain in prison for at least three years.

Do is not used in negative subjunctives.
e.g. We considered it desirable that he not leave school before finishing his exams.

Be has special subjunctive forms: I be, you be, etc.
e.g. It is important that Helen be present when we sign the papers.

Hi Kasie,
It's a very concise article that touches upon critical aspects of the Subjunctive Mood.
Kudos !!!