Täällä is used in opposition of tuolla. If both you and the person you are talking to are both in the area in which whatever or whomever you are talking about is located, the word täällä, "over here", is used. If neither one of you is in the same area as the person or the thing discussed but they are still close enough for you to point at them, the word tuolla, "over there", is used instead. Tässä and tuossa, on the other hand, are about things very close to you and you look at them from your own perspective alone.
What does this mean in practice? Let's say that you are looking at a large map for tourists at a market square looking for a museum you know is by that square. On that map there will very likely be a red dot that says Sinä olet tässä, "You are right here." Then one of your friends realises that she cannot find her phone. You notice that she has dropped it on the ground to a place which is just a step away from where you are standing. Se on tuossa!, "It is right there", you say kneeling down to pick up the phone, so that you can hand it over to her. You and your two friends are not very good at reading maps, so you separate to look for the museum. After a while, your friend starts walking towards you waving. Se on täällä, chartsman!, "It is over here, chartsman!", he shouts pointing at the pink building behind him. You walk to him, but you cannot see the third person in the party anywhere, so you call her. She answers her phone and you ask her whether she can see the pink building. Me olemme täällä!, "We are over here, can you see us?", you tell her waving your hand, so that she can see you. And then you go to the museum and worry about the map that helps you to navigate through an exhibition about maps. :)
Japanese is the next language to receive stories. Then Italian. :)
Plus there's this https://carex.uber.space/stories/index.html should any native Finns have time to help translate DL stories to Finnish. They even have stories in languages not available on DL yet.
@chartsman: The explanation by zzzzz is great. A shorter version is that the two words are different cases from the same stem. German has four cases where Finnish has over a dozen cases, the most of which are so called "lokativii" or location-related cases. Other examples are Helsinkiin, Helsingissä, Lontoon, Pariisiin (Sept 2020)
Nope. The meaning is "we are this one", and technically one could come up with a situation, like you have a bunch of pictures with groups of people, and you point out that our group is shown in this picture (and even then there would be better phrases to say...so it's quite far-fetched)
(Looking at it, the film "She's All That" is in Finnish "Sinussa on se jokin", back-translated "you have that something special" (literally "in you there is that something")
@Gregorius: I wouldn't use the translation of book titles or of film titles as references as in those translation processes other aspects than linguistic correctness often are more important. F/i the famous Russian book "Crime and Punishment" in Dutch has the title "Debt and Fine" .. not really a 1-1 translation. (Sept 2020)