According to Jewish Law, the deceased must be buried in the earth, and the body should be buried at least 40 inches under the ground, or 10 tefachim. We have a verse in the torah that says, "From it (the earth) you came, and to the earth you will return" (Bereishis 3:19). Specifically, the casket is placed in the very bottom of the grave. The lowering can be done either by the attendees, preferably family and friends, or, if need be, mechanical levers. Notably, this occurs during the service, and at all times everyone present should face the casket.

It is an extreme honor to the dead when a person participates in the shoveling of the dirt. This honorable duty is performed by family, Rabbunum (Rabbis) close friends, and, to a lesser extent, other members of the community. (Har Tzvi YD 267)

That said, people shoveling should be careful not to hand the shovel to each other, but rather insert it into earth after each use (Chachmas Adam 158:30, Beis Lechem Yehudah YD 376, Har Tzvi ibid.). Per Jewish Tradition, by not handing shovels from one family member to the next, the family is avoiding the symbol of death extending from one family member to the next. Why? Because it appears that your intention is to cause one pain , when you pass something to someone associated with death.)

Once the casket is placed in the ground, the attendees should fill in the grave until the casket no longer visible. Even on Yom Tov Sheni, Jews may fill the entire grave with dirt and make a mound on top, for this is the end of burial (Mishnah Berurah 526:28)

How surreal can this experience be? The deceased is being buried, leaving this world, and entering the next. While it may look like the end for the deceased, as evidenced by the burial, this is actually a new beginning. Not only for the deceased, but, on some level the burial experience resonates with the each and every attendee. Importantly, the end of the casket\burial is a new beginning for the mourner.