The subjunctive is not a verbal tense. It is a mood. Itis used when something is not real or it depends on something else. The subjunctive may be true or not or may happen or not:
Indicative: certain or objective things (used in tenses like present, past, future, conditional, etc.)
Subjunctive: possible or subjective things
The subjunctive does not use all the forms for the verb to be. It only uses be (present) and were (past) for all pronouns. Third-person singular does not add an -s for the rest of the verbs.
I demand that you be at work at 6 am.
I advised that he be at work at 6 am.
The boss requires that you be at work at 6 am.
Subjunctive 1 (English Club)
Subjunctive 2 (University of Bristol)
Subjunctive 3 (UsefulEnglish)
Subjunctive 4 (Lingolia)