This is the 23rd most frequent Spanish word.
todo
"Todo" means "everything" or "all" in English.
In this sentence, 'todo' is used as an indefinite pronoun referring to 'everything' or 'all of it', indicating that all aspects or items are ready.
Todo está listo para la reunión.
Everything is ready for the meeting.
Here, 'todo' is an adjective modifying the noun 'material', meaning 'all of the' study material.
He revisado todo el material de estudio.
I have reviewed all the study material.
In this example, 'todo' is part of a demonstrative expression 'todo aquel', referring to any and every individual who wishes to learn.