Il y a is idiomatic meaning “There is/are”, but how do you conjugate this in to different tenses? Well, you simply conjugate avoir (a) to the relevant tense using the “Il/Elle/On” form:
Present: Il y a – There is/are.
Imperfect: Il y avait – There were.
Passé composé: Il y a eu – There have been.
Future: Il y aura – There will be.
Conditional Present: Il y aurait – There would be.
Conditional Past: Il y aurait eu – There would have been.
Past perfect: Il y avait eu – There had been.
Future Perfect: Il y aura eu – There will have been.
Near Future: Il va y avoir – There is going to be.
Near past: Il vient d’y avoir – There has just been.