General tab

Smart Home and End
If checked, Home key moves cursor to first non-whitespace character on the line on first Home key press, and moves cursor to the first character on the line on second key press. Analogously End key moves cursor past last non-whitespace character on the line, and then past last character on next key press.
Enable auto indentation
If checked, pressing Enter key inserts line end character and whitespace to indent next line according to indentation settings.
Do not use tabs for indentation
If checked, spaces are used for indentation instead of tab character.
Tab key indents
If checked, Tab key inserts whitespace characters according to indentation settings to indent text at cursor. Otherwise Tab key only inserts single tab character.
Tab width
Displayed width of tab character in spaces. By default it is 8.
Indent width
Number of spaces inserted by single Tab key press. If tabs are used for indentation then Tab key inserts spaces until line indent is multiple of tab width, then it replaces spaces with tabs (if indent width is a multiple of tab width then only tab characters are used.)