The Basics of TeX (and LaTeX)

The backslash "\", is used to begin all TeX commands. (often called control sequences). There are two kinds of control sequences:

• control words are made up completely of letters. They must end with either a non-letter or a space so TeX knows where the control word ends. A space following a control word is "consumed" by TeX and does not appear in the output. An example is the control word \bf, which prints subsequent text in boldface.
• control symbols consist of the backslash followed by exactly one non-letter. They are most often used to put a special symbol in the text. For example \$ prints a $ (which cannot be entered directly because TeX uses it to begin math mode). Control symbols do not have to be followed by a space.

TeX commands are case-sensitive. Most are all lowercase, although a few commands do use the first letter in uppercase, such as \Delta (for an uppercase delta). Even fewer commands use all uppercase.

TeX uses grouping to limit the effect of certain commands. Braces ({ and }) are used to begin and end groups. For example, {}bf these words will be boldface\ limits the boldface text to the words that appear within the braces.

TeX recognizes the following units in its commands that require measurements:

 
   cm   centimeter    pt    printer's point, approx 72 per inch
   mm   millimeter    em    font dependent width of "m"
   in   inch          ex    font dependent height of "x"

When TeX builds a page, it considers all of the parts (words, lines, paragraphs, etc.) to be different sized boxes. TeX starts with a simple box, an individual letter, and then builds words, which are considered to be hboxes (horizontal boxes). The words are then put together with "glue" to form a line, which results in a larger hbox. A group of these hboxes -- stacked together vertically with more "glue" between them -- form a vbox (vertical box). A page is a large vbox made up of several smaller ones.

You do not normally need to be concerned with this, but sometimes (such as when an error message refers to an "overfull hbox") it is helpful to know how TeX works.

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