"Mara is near you."
Translation:SoHDaq Sum mara.
Why not "mara'e" here? I'm confused at how this sentence breaks down - what is functioning as the verb?
Sum is a regular verb in Klingon. In English it is an adjective and so needs the connecting verb "is" to connect it to a noun. However, in Klingon, since it is already a verb we can just put the subject noun in the right place without any markings (like -'e') or connecting words. The -'e' topic marker is only required when using a pronoun to connect two nouns. There is no pronoun being used here, so -'e' is not required.
What jdmcowan said. You'll understand it better if you think of sentences based on pronouns as a different kind of sentence than sentences based on verbs. That is, a sentence like tlhIngan ghaH mara'e' Mara is a Klingon is a "to be" kind of sentence, and these are different than basic sentences like SoHDaq Sum mara Mara is near you, which are based on actual verbs.
Don't get into the habit of thinking of pronouns as verbs — they're not.
"To be" sentences that end in a noun or noun phrase require -'e'. It's just a rule to follow. Basic sentences do not require -'e' on the subject. If you put -'e' on the subject of a basic sentence, you are adding focus or emphasis to it: SoHDaq Sum mara'e' MARA (not somebody else) is near you.