Ellipses are used in informal and formal writing.
If you want to express a pause or a trailing off in your writing, use an ellipsis. An ellipsis is always three dots, but if you put an ellipsis at the end of a sentence you need to use a period as well (for a total of four dots).
You can choose whether or not to place a space between the ellipsis and your words.
Is that a…scorpion?
Is that a … scorpion?
I once wished that…. Actually, never mind.
I once wished that … . Actually, never mind.
Ellipses are used to indicate that you’ve removed part of a quote. Some writers enclose these ellipses in brackets, and some don’t.
Some style guides use ellipses at the end of quotes, and some don’t.
“We shall go on to the end, we shall fight in France, we shall fight on the seas and oceans, … we shall fight on the beaches. …”
“We shall go on to the end, we shall fight in France, we shall fight on the seas and oceans, […] we shall fight on the beaches.”