The two forms sometimes called "subjunctive" in English grammar, are very different in their usage and frequency.
The so-called "past subjunctive" is identical with the simple past in every case except "were" vs "was". It is normally used in writing in counter-factual conditionals ("If he were"; "I wish I were"). Some people use it in speech, but many do not.
The so-called present subjunctive is indistinguishable from the base form of the verb in all cases. The only common use of it is in formal contexts of meetings and committees, after verbs like "resolve", "decide", "mandate". eg "The committee resolved that the matter be discussed at the next full meeting". Many people prefer to use a modal instead, such as "that the matter should be discussed".
I believe that it is unhelpful to refer to this as "subjunctive" at all, and prefer to call it a use of the base form, or infinitive (without 'to').
The other use of the present subjunctive is archaic: it is only used in a few set phrases (notably "Long live X"), and for deliberate archaism (eg "If he be the rightful king").