3. Perfect Tenses
have done, will have been doing, will have done, must/should have done,
In Russian it's much simpler: roughly compared to the English grammar
either simple or continuous forms.
Or more Russian-grammarly like: perfective (result, finished action) vs imperfective (process) aspects of the verb.
Perfective forms often (but not always!) have prefixes: сделал, пришёл, поел, приехал = did
imperfective: делал, шёл, ел, ехал = was doing.
It applies to future and past tenses.
While in Present tense: it's mostly just one form of verb (forget about motion verbs, they will come later)
I buy vs. I am buying = Я покупаю
now? or in general? No clue - the context & additional words will clear things out.