An ellipsis is formed by three periods/dots put together. Use a space between each dot and before and after the whole ellipsis. (Plural is ellipses.)
Uses: indication of the omission of a word from a sentence, a group of words from a longer quote, or a while section out of a longer section, to shorten a sentence, add a slight pause in speech, show dramatic effect, and silence or to add a pause, and add an unfinished thought.
Ex. If you should find this diary, will you please keep it safe for me, because some day I hope. . . .