"It is a different word."
Translation:Je to jiné slovo.
Actually: "To je jiné slovo." and "Ono je to jiné slovo." are very similar.
To is here something indeterminate in the "To je/jsou.." common type of sentence.
Ono in "Ono je jiné slovo." does not really work. We would just wonder which ono? This pronoun works fine in phrases like "Ono slovo je jiné."/"That word is different.".
You could make this sentence stronger with "Ono je to jiné slovo." but notice the "to" there. It is really necessary.
I think this is one of those "That's just how it's used" things. As I understand, in general, you use "to je" and "to jsou" when you would normally say "it is" or "they are" in English -- when you mean a sort of general "it" or "they." A moderator could probably offer a clearer explanation!
Adjectives are placed in front of the noun.
(Unless it's scientific terminology (like 'sulphuric acid' = 'kyselina sírová') or in very specific situations where the adjective is placed after the noun for additional emphasis, but that's definitely not something you should care about at your level.)
I am learning, too, but... Both words can have the meaning "other" in English However, with "další" it is "other" in the sense of "additional," while for "jiný," it's "other" in the sense of "different." I hope this helps, but maybe a moderator will give you a better explanation!
In this sentence, the English "that" is part of the widely-used Czech To je/Je to construction, which is generally translated as "It is/That is." The English "that" here does not modify the noun, as it would in your suggested sentence. I don't think that your sentence -- It is that different word -- would be used much on its own, either.
Your sentence would be "That word is different." While the ultimate meanings of "That word is different" and "It/That is a different word" are very similar, they have different grammatical structures in both languages, and the course consistently distinguishes between them.
ETA: Also, just for future reference, "Ona je hezký" is incorrect. Since ona is feminine, the adjective needs to be feminine, too (hezká).