Re-format text blocks to wrap to a fixed character width

1. Set the text width in characters :set textwidth=80
2. Select the lines of text you want to re-format v to use visual selection
3. Reformat gq
4. To reformat a single paragraph without selecting it first {gq}

Turn on (or off) line numbering

1. To turn on line numbering, at the : prompt type set number
2. To turn off line numbering, type the command set nonumber
3. To set relative line numbers set relativenumber