Used to indicate that something is necessary or that a certain condition must be met for something else to happen.
지 and 만 are there just to add emphasis and neither is required.
It can be used to end a sentence by using 지 for casual or 지요 for polite. The meaning changes though telling the person or reminding them that something needs to be done.
Nouns can also use the form (이)라야(만)