The second conditional usually describes an unrealA tense that expresses a hypothetical situation. E.g.: I wish you were here. situation with reference to the present. We imagine a hypotheticalUnreal, imagined. situation, which is in contrast with the real situation in the present.

if-clause with past simple or continuous
main clause with would + infinitive (simple or continuous)

Note that here it is only the form of the past simple or continuous that we use. Remember the phrase If I were you…, where were is obviously not the past form of be in the first person singular. Were in this case is the past subjunctive form of be. Although this is what prescriptive grammar dictates, for many native speakers of English, nowadays, it is becoming common to use was instead of were in the first and third person singular. Note that were sounds more formalNot belonging to colloquial or everyday speech; official. E.g.: I demand that Mr Smith call the person on whom the committee has decided..

If I had some cigarettes, I would give you one.
I would be surprised if she weren't/wasn't still sitting there.

In some cases, the second conditional can express a theoretically possible but unlikely situation. This can refer to future timeA concept which is related to our perception of reality; that part of existence which is measured in seconds, minutes, hours, days, weeks, etc..

If the Third World War broke out, it would mean the end of humankind.

Some sentences may look like a second conditional but in fact are not:

If he was hungry, he would always run to the nearest take-away.

This is actually a zero conditional, where would in the main clause expresses a past habit and if means when or whenever.

The difference between the zero and the first conditional
IF-sentences and conditionals Third conditional