These three little dots can cause quite a bit of confusion amongst authors.
According to The Chicago Manual of Style (Sixteenth Edition), 'An ellipsis is the omission of a word, phrase, line, paragraph, or more from a quoted passage.' Such an omission is indicated by three periods which are commonly known as ellipses. The same three dots can be used as suspension points to indicate faltering or interrupted speech.
Just three. Using more points will not make the pause longer or more dramatic.
Whether you are using ellipses or suspension points, within text, they are spaced on both sides. If you are following The Chicago Manual of Style (CMOS) then the periods are also spaced. If you are following New Hart's Rules (NHR) then the periods are not spaced.
'No . . . I mean, yes.' (CMOS)
'No ... I mean, yes.' (NHR)
Rather than typing three separate periods, they can be set as a single character using unicode U+2026 or ctrl + alt + full point in Word. Some publishers prefer the narrower spaces between points that this provides.
When ellipses and suspension points are used at the end of a sentence they are spaced after the preceding word but there is no space between them and any following punctuation. A fourth full point is not used to indicate the end of a sentence, neither is a comma used at the end of dialogue.
I'm not sure ...
'It's possible ...' Ben said.
If the sentence ends in a question mark or an exclamation mark then these are retained after the ellipses.
'Do you think you could though ...?'
'He couldn't have survived ...!'
Do not use suspension points when the dialogue is interrupted rather than trailing off. To indicate an interruption, use the em-rule/em-dash.
'I was just about to—'
'I don't care what you were just about to do!'
Other articles in the Self-editing for Self-publishers series:
Basic Rules for Punctuating Dialogue
The Show/Hide Button in Word
Paragraph Styles for Non-fiction and Fiction
Double to Single Spacing