This is the 2559th most frequent Polish word.
przeczytaj
"Przeczytaj" means "Read (imperative form)."
The word 'przeczytaj' is used here as an imperative form, instructing someone to perform the action of reading.
Przeczytaj tę książkę w wolnym czasie.
Read this book in your free time.
The word 'przeczytał' is a past tense form, indicating that Marcin has completed the action of reading.
Marcin przeczytał już trzy rozdziały.
Marcin has already read three chapters.
The word 'przeczytać' here is used in its infinitive form within a polite question, asking someone to perform the action of reading aloud.