Suppose your ASL Linguistics professor gave you an assignment to watch a video, state which verb is signed, for each verb identified, detail the semantic information added to the discourse.

Now suppose you have no real clue what your professor is asking you to do. 

Let's discuss your instructor's assignment a bit and see if we can figure out what they want.

"Discourse" is a fancy word that means "talking or writing a lot about something. It's like when you have a conversation with someone, tell a story, or write an essay. In other words, "discourse" is just a way to describe communication that happens in bigger chunks than just a word or a sentence.  Discourse is about longer talks or pieces of writing.  We could say that "discourse" refers to any form of spoken or written communication involving extended expression of thought.

The word "semantic" is often just a fancy way of saying "meaning."

"Semantic information" is just a fancy way of saying "information that has meaning" which is a fancy way of saying information. (Because if information doesn't have meaning then it really isn't information is it?)

English written language: "kitty" has meaning.

English written language: "KITTTYYYYY!!!! Has the same basic meaning but also has additional semantic information (the additional meaning carried by the capitalization and the exclamation points). That additional semantic information conveys the meaning that someone is very excited (or experiencing some other heightened emotional state) about a kitty.

When you observe a verb being signed in ASL you can ask yourself:
"What extra meaning is added to the basic meaning of the (verb) sign to your conversation or statement?"

Sometimes the answer is "none."
"Plain verbs" don't add EXTRA meaning beyond the basic meaning of the verb. That's why we call them plain.

Example:  Someone signs an uninflected, basic version of the sign: RUN
Verb: RUN
Type: Plain
Semantic information added to the discourse: States the basic action of running (as in a person using their legs to move quickly across a surface). Doesn't add any extra semantic meaning beyond the dictionary or citation meaning of the sign RUN.

Example: Someone signing "I handed it to her" using location and direction to inflect the sign GIVE].
Verb: GIVE, inflected as: PRO1-GIVE-PRO3 (or: me-GIVE-her) (the sign starts near the body and moves toward the object) ("I gave her")
Type: Indicating
Semantic information added to the discourse: The verb GIVE was inflected to add (or "indicate") the subject and the object of the verb. More specifically it added the meanings of a first-person pronoun (I/me) and a third-person pronoun he/she/that-person.

[Video shows someone signing "I had surgery on my shoulder" using an "A" handshape and done on the shoulder]
Verb: SURGERY, inflected as SURGERY-on-the-shoulder
Type: Depictive
Semantic information added to the discourse: The handshape of this sign indicated the use of a cutting instrument such as a scalpel or other knife or tool commonly associated in ASL with the act of surgery. The location of the sign added the meaning of "at the location of the shoulder."