What is the meaning of -을?

indicates the direct object of a verb

Accusative case marker.

The accusative particle, indicating the direct object of a verb.

In "long negation" constructions with (-ji), attaches to the negated verb to add emphasis.

Indicates the indirect object of a verb.

A verbal and adjectival irrealis adnominal suffix; generally equivalent to English "that [one] will" or "who [one] will", but not always with a future meaning; indicates the future intention of the subject, the inference of the subject about an event (whether past, present, or future), a general timeless fact, something that ought to be done, etc.

Source: wiktionary.org