The Levites Today
1. Holiness. The sons of Levi were set apart to perform the holy service. It is an affirmative command for the Levites to be available and prepared to serve in the Temple. The role and laws of the Levites and the Kohanim (who are sometimes called Levites by the Torah) is discussed by Maimonides in his section concerning the vessels of the Temple. A Levite is a holy vessel. The ideal of each Levite is to be doing holy service, the ultimate of which is the Service in the Holy Temple in Jerusalem.
Levites have an extra measure of holiness. Though they are permitted to come into contact with the dead, in contrast to Kohanim, at the time of the Temple they were instructed to avoid impurity. When the time will come for the purification of the tribes of Israel, the tribe of Levi will be purified first.
2. Genealogy. A Levite is one who is born of a father whose lineage reaches back to Levi, son of Jacob. All families of Jews have an assumed proper lineage unless there is a reason to suspect otherwise; this assumption of unbroken lineage applies to Kohanim and Levites as well.
Common names of Levite families today include Levy, Levin, Lewis, etc.
A Levite does not have the marriage restrictions of a Kohen. He may choose a marriage partner subject to the same qualifications as any other Jew. He may marry the daughter of a Kohen, Levi, or Israelite, including a convert, divorcee, or daughter of a profaned Kohen.
3. Assisting the Kohanim. In the Temple, one of the major functions of the Levites was to assist the Kohanim in the performance of the Temple service. Today, the Levites pour water over the hands of the Kohanim who are about to give the Birkat Kohanim in the synagogue. This is to recall their role in the Temple service, although it was not actually one of their tasks in the Temple. The Zohar relates that this washing adds the Levite's holiness to that of the Kohen, helping the blessing to be properly delivered in God's honor.
4. Aliya to the Torah. A Levite receives the second aliyah to the Torah, with a Kohen receiving the first. This is to give honor and avoid quarrels. If no Kohen is present, a Levite is not called. A Levite may also receive the maftir or an acharon (additional after the set order of seven) aliyah.
5. Levitical exemptions. The firstborn son of a Levite or a woman whose father was a Levite is exempt from the requirement of Pidyon HaBen (redemption of the firstborn). This is due to the fact that the Levites took the place of the firstborn of Israel and the tribe as a whole was redeemed at that time. Similarly, they need not redeem the firstborn of their donkeys.
Upon slaughtering an animal for his own use, a Israelite must give a portion of the meet to the Kohanim, however the Levites are exempt from this Kohanic gift.