You can describe something as abstruse if you find it highly complicated and difficult to understand.

If someone is addled by something, they are confused by it and unable to think properly.

When you adduce, you give facts and examples in order to prove that something is true.

If you describe something as ambiguous, you mean that it is unclear or confusing because it can be understood in multiple ways.

Something that is arcane is mysterious and secret, known and understood by only a few people.

If something confounds you, it makes you feel surprised and confused, often because it does not meet your predefined expectations.

A conundrum is a problem or puzzle that is difficult or impossible to solve.

When you decipher a message or piece of writing, you work out what it says, even though it is very difficult to read or understand.

A denouement is the end of a book, play, or series of events when everything is explained and comes to a conclusion.

A dilemma is a difficult choice between two equal alternatives.

To divulge something is to reveal information that was once private or secret.

When you speak in an eloquent fashion, you speak beautifully in an expressive way that is convincing to an audience.

Someone or something that is enigmatic is mysterious and difficult to understand.

When you enunciate, you speak or state something clearly so that you can be easily understood.

When people equivocate, they avoid making a clear statement; they are deliberately vague in order to avoid giving a direct answer to a question.

If you evince particular feelings, qualities, or attitudes, you show them, often clearly.

Exegesis is a detailed explanation or interpretation of a piece of writing, especially a religious one.

One thing that exemplifies another serves as an example of it, illustrates it, or demonstrates it.

To explicate an idea or plan is to make it clear by explaining it.

An exposition is a detailed explanation or setting forth of an idea, theory, or problem, either in a written or spoken format.

When you expound something, you explain it in great detail, often taking a while to do so.

If you fathom something complicated or mysterious, you are able to understand it.

A garbled message or speech is confusing and not understandable, often because it is spoken in a hurry or is communicated with lots of accompanying noise.

If you gloss a difficult word, phrase, or other text, you provide an explanation for it in the form of a note.

An impenetrable barrier cannot be gotten through by any means; this word can refer to parts of a building such as walls and doors—or to a problem of some kind that cannot be solved.

If an idea or thought is incisive, it is expressed in a penetrating and knowledgeable manner that is clear and brief; additionally, it can demonstrate impressive understanding of related ideas or thoughts.

Someone who is speaking in an incoherent fashion cannot be understood or is very hard to understand.

If someone is lucid, they are able to understand things and think clearly; this adjective also describes writing or speech that is crystal clear and easy to understand.

If you describe something as nebulous, you mean that it is unclear, vague, and not clearly defined; a shape that is nebulous has no clear boundaries.

To obfuscate something is to make it deliberately unclear, confusing, and difficult to understand.

An oblique statement is not straightforward or direct; rather, it is purposely roundabout, vague, or misleading.

Someone is obtuse when they are slow to understand things; someone can choose to be obtuse when they deliberately do not try to figure things out.

Something is opaque if it is either difficult to understand or is not transparent.

A paradox is a statement that appears to be self-contradictory or unrealistic but may surprisingly express a possible truth.

A parenthetical remark further explains or qualifies information.

The art of pedagogy is the methods used by a teacher to teach a subject.

Someone who demonstrates perspicacity notices or understands things very quickly.

Recondite areas of knowledge are those that are very difficult to understand and/or are not known by many people.

A subtle point is so clever or small that it is hard to notice or understand; it can also be very wise or deep in meaning.

Something that is turbid, such as water, is muddy or cloudy because it has lots of small pieces of matter or dirt in it.