While shifting blocks of text is most important for programmers (See Features for Programming), it is also useful for other tasks, such as creating indented paragraphs.
To shift a block of text one tab stop to the right, select the text, then choose Shift Right from the Edit menu. Note that the accelerator keys for these menu items are Ctrl+9 and Ctrl+0, which correspond to the right and left parenthesis on most keyboards. Remember them as adjusting the text in the direction pointed to by the parenthesis character. Holding the Shift key while selecting either Shift Left or Shift Right will shift the text by one character.
It is also possible to shift blocks of text by selecting the text rectangularly, and dragging it left or right (and up or down as well). Using a rectangular selection also causes tabs within the selection to be recalculated and substituted, such that the non-whitespace characters remain stationary with respect to the selection.
Text filling using the Fill Paragraph command in the Edit menu is one of the most important concepts in XNEdit. And it will be well worth your while to understand how to use it properly.
In plain text files, unlike word-processor files, there is no way to tell which lines are continuations of other lines, and which lines are meant to be separate, because there is no distinction in meaning between newline characters which separate lines in a paragraph, and ones which separate paragraphs from other text. This makes it impossible for a text editor like XNEdit to tell parts of the text which belong together as a paragraph from carefully arranged individual lines.
In continuous wrap mode (Preferences -> Wrap -> Continuous), lines automatically wrap and unwrap themselves to line up properly at the right margin. In this mode, you simply omit the newlines within paragraphs and let XNEdit make the line breaks as needed. Unfortunately, continuous wrap mode is not appropriate in the majority of situations, because files with extremely long lines are not common under Unix and may not be compatible with all tools, and because you can't achieve effects like indented sections, columns, or program comments, and still take advantage of the automatic wrapping.
Without continuous wrapping, paragraph filling is not entirely automatic. Auto-Newline wrapping keeps paragraphs lined up as you type, but once entered, XNEdit can no longer distinguish newlines which join wrapped text, and newlines which must be preserved. Therefore, editing in the middle of a paragraph will often leave the right margin messy and uneven.
Since XNEdit can't act automatically to keep your text lined up, you need to tell it explicitly where to operate, and that is what Fill Paragraph is for. It arranges lines to fill the space between two margins, wrapping the lines neatly at word boundaries. Normally, the left margin for filling is inferred from the text being filled. The first line of each paragraph is considered special, and its left indentation is maintained separately from the remaining lines (for leading indents, bullet points, numbered paragraphs, etc.). Otherwise, the left margin is determined by the furthest left non-whitespace character. The right margin is either the Wrap Margin, set in the preferences menu (by default, the right edge of the window), or can also be chosen on the fly by using a rectangular selection (see below).
There are three ways to use Fill Paragraph. The simplest is, while you are typing text, and there is no selection, simply select Fill Paragraph (or type Ctrl+J), and XNEdit will arrange the text in the paragraph adjacent to the cursor. A paragraph, in this case, means an area of text delimited by blank lines.
The second way to use Fill Paragraph is with a selection. If you select a range of text and then chose Fill Paragraph, all of the text in the selection will be filled. Again, continuous text between blank lines is interpreted as paragraphs and filled individually, respecting leading indents and blank lines.
The third, and most versatile, way to use Fill Paragraph is with a rectangular selection. Fill Paragraph treats rectangular selections differently from other commands. Instead of simply filling the text inside the rectangular selection, XNEdit interprets the right edge of the selection as the requested wrap margin. Text to the left of the selection is not disturbed (the usual interpretation of a rectangular selection), but text to the right of the selection is included in the operation and is pulled in to the selected region. This method enables you to fill text to an arbitrary right margin, without going back and forth to the wrap-margin dialog, as well as to exclude text to the left of the selection such as comment bars or other text columns.