This is the most common style of justification (at least for English). Lines are aligned at the left margin but left uneven at the right.

This aligns each line with the right margin. Spaces and tabs are added on the left, if necessary, to make lines line up on the right.

This justifies the text, aligning both edges of each line. Justified text looks very nice in a printed book, where the spaces can all be adjusted equally, but it does not look as nice with a fixed-width font on the screen. Perhaps a future version of Emacs will be able to adjust the width of spaces in a line to achieve elegant justification.

This centers every line between the current margins.

This turns off filling entirely. Each line will remain as you wrote it; the fill and auto-fill functions will have no effect on text which has this setting. You can, however, still indent the left margin. In unfilled regions, all newlines are treated as hard newlines (see Hard and Soft Newlines) .

Make the region left-filled (set-justification-left).