"Who are you?"
Translation:Kiu estas vi?
This might help you. They are all derived in a regular manner from prefixes and suffixes: https://en.wikipedia.org/wiki/Esperanto_vocabulary#Table_of_correlatives
It is used in yes/no questions and in "pick one" questions of the kind Ĉu vi volas kafon aŭ teon? "Do you want coffee or tea?"
It's not used in WH questions with a question word such as "who, how, where, what, why, how many, when". (In Esperanto, those might perhaps be called KI questions.)
Ekspliko is a word that I barely encountered in 20 years of speaking Esperanto. Now I'm seeing it everywhere among new speakers. I wonder if it got listed in Google Translate, Tatoeba, or some other online dictionary. It's a rare word - roughly equivalent to "to explicate".
The normal word for "explanation" is klarigo.
In English grammar, a "predicate" is a verb with all its modifiers. The English term is "predicate nominative" for the noun complement of the verb "to be" which is, of course, in the nominative case. We often help people understand by showing how we can replace the form of "to be" with an = sign between the two nouns.
When I was at school, "to be" sentences were analysed as "subject + copula + predicate". But it's possible that I am misremembering; that that terminology is outdated; or that there are multiple competing theories of analysing English (sadly all too frequent in English, in my experience).
Thank you for your comment; after reading up on Wikipedia briefly, I see that my use of "predicate" is, at best, a minority usage, and "predicative expression" and "predicat(iv)e adjective"/"predicat(iv)e nominal" would seem to be better.
I have encountered the idea of "copula" when studying Irish, which I grew up calling a linking verb. I had not heard predicate used that way before, but I am from the US and it could be that British use that? I see that you can analyze sentences in the field of logic using predicate in that way. It is interesting that in some languages they explain the situation as having two subjects that complement each other. http://www.merriam-webster.com/dictionary/predicate
Edit: I have since posted to Rae.F and found that she was talking about the word copula which is definitely a linguistics term. The second definition of predicate is a linguistics term also.