I'll try to explain this as simply as possible, since subjunctive mood in English is one of the worst-described parts of grammar. You have several "moods" in English. Indicative (real events), imperative (commands/directions) and subjunctive (hypothetical or conceived events). Some people put "questions" into its own category: interrogative. So, subjunctive mood is used when the event is not a real thing, but conceived in the mind. For example, "I demand that he talk to me!" The form of "(that) he talk" indicates this is not an actual event which happens, but just one's own imagination. There's a lot of overlap in the verb form between subjunctive and indicative, so you can only recognise present subjunctive in third person (he/she/it). If you're ever confused, rewrite the sentence in the passive form and by using "to be", you'll clearly see if the subjunctive form needs attention. Compare "I demand that he be talked to!"(correct) and "I demand that he is talked to!"(complete nonsense) Second and third conditionals in English use the subjunctive form: if I were... if I had been... For "if he talked..." in a conditional, the past tense is actually subjunctive, and not indicative past tense. Again, you'll only spot a clear difference in rare cases. The big danger is in thinking that you could always use the simple indicative form. You can also use word order to indicate a subjunctive mood: "had he known, he would have helped us". "Had he known" is equivalent to "if he had known". "He had known" by itself is a statement of fact, and therefore indicative. For future tense, it's even trickier to explain. I'm happy to argue that by using "will (verb)", that is already a subjunctive form... you can't predict the future; only be sure to varying degrees. Brajesh's example from wikipedia ("if I were to go") is another possible example, but a little confusing to explain because some subjunctive forms are created by putting the event in the past (viz. 2nd/3rd conditionals). Hope that helped a bit.

The subjunctive in Modern English occurs in a variety of contexts in which the form of the verb used is different from what it normally would be, given the implied time of the action. Regardless of the subject, the form of the present subjunctive verb used to express present or past desires and the like in that clauses is the bare form of the infinitive (not preceded by "to"). Hence, the present subjunctive of "to go" is "I go", "you go", "he/she/it go", "we go", "they go". For instance: "It was required that he go to the back of the line" (compared with the indicative "Everyone knows that he went to the back of the line"); "It is required that he go to the back of the line" (compared with the indicative "Everyone knows that he goes to the back of the line"). The English subjunctive also occurs in counterfactual dependent clauses, using a form of the verb that in the indicative would indicate a time of action prior to the one implied by the subjunctive. It is called the past subjunctive when referring counterfactually to the present, and is called the pluperfect subjunctive when referring counterfactually to the past. It occurs in that clauses following the main-clause verb "wish" ("I wish that she were here now"; I wish that she had been here yesterday") and in if clauses expressing a condition that does not or did not hold ("If she were here right now, ..."; "If she had been here yesterday, ..."). A form of the subjunctive, called the future subjunctive, is used in if clauses of doubtful possibility with future reference; regardless of person and number, it uses the form "if I were to go". The terms "present subjunctive" and "past subjunctive", such as appear in the following table, refer to the form and not to the time of action expressed. (Not shown in the table is the pluperfect subjunctive, which uses the had plus past participle construction when the counterfactual time of action is the past.) will be if I were to be if he/she/it were to be if we/you/they were to be I am not he/she/it is not we/you/they are not that I not be that he/she/it not be that we/you/they not be Time of action present or future past, present or future past present future future present or future past, present or future Usage desire in that clauses counterfactuality in if clauses or in that clauses after wish doubtful possibility in if clauses desire in that clauses -----------------------from wikipedia.com

A form of the subjunctive, called the future subjunctive, is used in if clauses of doubtful possibility with future reference; regardless of person and number, it uses the form "if I were to go".