I understand that "jen" means "behold" or "here is" and I see it used often. But is it ever proper to use "tie ĉi estas", and what's the difference between the two? When should I use "jen" and when should I use "tie ĉi estas"?
Jen is an exclamation: "Look! behold! here is/are; there is/are"
Tie ĉi estas is an explanation: "This is..."
- Altiri la rigardon sur iun aŭ ion
Attract the attention onto someone or something.
- Prezenti pli vigle ian subitan okazaĵon
Present some sudden occasion more lively/strongly.
- jen la ĝusta tempo por lin kapti
It's the right time to capture him.
- krak! jen ĝi falis de la ŝranko
Crack! It fell from the cabinent.
- jen mi estas!
Here I am!
I usually use jen when I'm trying to present something: a new project, an article, something I lost and just found.
- Jen mia dormĉambro! Estu ĵaluza ĉar tiel bela ĝi estas!
And here is my bedroom! Be jealous because it is so beautiful!
Ĉi tie estas is something I would say giving somebody a tour of the house.
- Ĉi tie estas la dormĉambro, la banĉambro...
Here is the bedroom, the bathroom...
I think of "jen" as existing primarily to draw someone's attention to the word(s) after it, while "ĉi tie" is setting you up for stating facts about the location of something. "Jen" is sort of like how we use the French-derived "Voilà!" in English (I assume French speakers use it that way too, but I don't speak French...)
Jen la kato = draws more attention to the fact that there is a cat. This could be translated as "behold the cat; here's the cat; there's the cat; this is the cat; look at the cat; observe the cat; notice the cat"
Ĉi tie estas la kato = draws more attention to the fact that the location of the cat is "here". Translates to "here is the cat."
Much more loosely translated/expanded examples, for emphasis:
Jen mia domo = Here is my house! (Welcome! Voilà! What do you think of it?)
Ĉi tie estas mia domo = Here is my house. (If you were wondering where my house is or which one is mine, it's this one here.)
I tend to think of "jen" being used in situations where you might also use "rigardu, spektu, vidu" though that isn't always the case.
I recommend not saying "Tie ĉi estas ...", when "Jen ..." does the job. "Tie ĉi estas ..." you say, if you need to emphasize that something is "here" so at this very place. While thinking about examples I tend to put "tie ĉi" rather to the end of the sentence in these cases.
Ne indas telefoni al via patro. Li estas tie ĉi.
(It's not worth while calling your father. He is right here.)