The korean language foesn't really use pronouns in the same way as English, and it's more common to describe people by title or omit pronouns altogether. Also a lot of the sentences in Duolingo do use "he", "she", "they" and "we"? (그, 그녀, 그들/그녀들, 우리) I think of these only 우리 is commonly used as pronouns (?) And it should be noted that apparently the word for "she" sounds rude and is therefore should be avoided
I'm a beginner
The base verb (to be like that) is 저렇다
저래요 Means 'it is like that' and is a mid formality level declaritive conjugation of the verb.
작다 -> 작아요 (to be small -> is small) 춥다 -> 추워요 (To be cold -> is cold)
저렇지 않아요. Is part of the negative form of the same level of conjugation. Note that negation can be done in two ways by either adding 안 before the positive conjugation of the verb, or 지 않아요 after the base form.
안 저래요 = 저렇지 않아요 = (It's) not like that. 안 작아요 = 작지 않아요 = (It's) not small
All the forms you mentioned should exist as conjugations of 이렇다 and 그렇다
The adjective is a ㅎ-irregular one. Other determiner adjectives and native Korean color adjectives are also ㅎ-irregulars. Note that not all stems that end in ㅎ are not irregulars. See 좋다.
When conjugating these adjectives to the casual or polite form, the final ㅎ drops and the final vowel of the stem changes. If the final vowel is ㅓ or ㅏ, the final vowel becomes ㅐ. If the final vowel is ㅑ, the final vowel becomes ㅒ.
So conjugating 저렇다 into the polite form can be broken down:
저렇다 → 저러 + 어요 → 저래요
The most casual form of 않다 is 않아. If you're asking about "to sit" (which is a different verb, 앉다), the most casual form would be 앉아. The verb 않다 is actually not used in command form, and it's replaced with the verb 말다. The way to used it as a command depends on what politeness level you want to use.