"The spy returns to the underground base."
Translation:wutlh waw' chegh ghoqwI'.
Klingon does not have adjectives. Nouns can be modified in a few ways. One way is to put a verb indicating a quality after the noun. Another way is to put a -meH clause in front of it. Or you could put it inside a -bogh clause. And yet another way is to put another noun in front of it.
When you put a noun in front of a noun, this is called a noun-noun construction. The first noun modifies the sense of the second noun. This might mean possession, like ghoqwI' HIch spy's pistol, or it might mean the first noun is narrowing the type of the second noun. This last meaning is what's happening here.
wutlh waw' is a waw base. What kind of waw? A wutlh waw' underground base.
This course talks about "adjectives," but it is wrong to do so. There are many ways to modify nouns in the manner of an adjective, but there is no part of speech specifically meant to do so.
waw''a' important base (modifies the noun with a suffix)
waw' pegh secret base (modifies the noun with a verb of quality)
wutlh waw' underground base (modifies the noun with another noun)
waw' SamlaHbe'bogh jagh base which the enemy cannot find (modifies the noun with a relative clause)
turmeH waw' mission base, base for conducting a mission (modifies the noun with a purpose clause)