The Messianic Redemption will be ushered in by a person, a human leader, a descendant of Kings David and Solomon, who will reinstate the Davidic royal dynasty. According to tradition, Moshiach will be wiser than Solomon, and a prophet around the level of Moses.
Ever since the destruction of the Holy Temple, in every generation there is an individual, a scion of the House of David, who has the potential to be the Moshiach. If at any moment the Jews are worthy of redemption, this person would be directed from Above to assume the role of the redeemer.
In every generation there is a scion of the House of David who has the potential to be the MoshiachDuring the Messianic Era, the Moshiach will serve a dual role. He will be a monarch, ruling over all of humanity with kindness and justice, and upholding the law of the Torah—613 commandments for the Jews, and seven for the non-Jews. He will also be the ultimate teacher, the conduit for the deepest and most profound dimensions of the Torah which will then be revealed by G‑d.
How are we to identify the Moshiach?
Moshiach is not identified by his ability to perform earth-shattering miracles. In fact, he isn't required to perform any miracles at all (although the performance of miracles doesn't disqualify him either).
The following are the criteria for identifying the Moshiach, as written by Maimonides:
If we see a Jewish leader who (a) toils in the study of Torah and is meticulous about the observance of the mitzvot, (b) influences the Jews to follow the ways of the Torah and (c) wages the "battles of G‑d"—such a person is the "presumptive Moshiach."
If the person succeeded in all these endeavors, and then rebuilds the Holy Temple in Jerusalem and facilitates the ingathering of the Jews to the Land of Israel—then we are certain that he is the Moshiach.