What do they mean?
 

It may sound and look stupid, but I don't get these lines:

Date of death : He passed over the sea in the year 120 of the Fourth Age

After the death of Kind Elessar, he passed over the Sea and it is said that he took Gimli with him.

It says that Legolas died orsomething, but what do they mean passed over the seas? Did he sailed over the seas untill he died?

Legolas and Gimli passed west over the sea to the Undying Lands. The same place that Frodo, Bilbo and the rest were headed when they left the Havens. Legolas and Gimli set sail from Ithilien via Anduin though.

After King Elessar (Aragorn) died, Legolas sailed to the Undying Lands as elves are wont, and he took Gimli the Dwarf.

Legolas, however, did not die - at least not until the end of the world - as he was immortal and would therefore live as long as Arda endured.

Gimli (assuming that he made it there), along with Bilbo, Sam and Frodo, did all die in Aman since, although they were called the Undying Lands, mortals could not gain immortality by simply by going there.

Thnx Sauce, that was all I needed to know!