• A source file is made up of text, formulas, and instructions (commands) to $\LaTeX.$
• Commands start with a backslash (\) and tells $\LaTeX$ something special.
• One-line comments start with %.
• $\LaTeX$ disregards the way you input and position the text, and follows only the formating instructions given by the commands.
• $\LaTeX$ notices when you put a blank space in the text, but it ignores how many blank spaces have been typed.
• There are two kinds of math formulas and environments

　　　　-----Inline formulas; they open and close with $ or open with \( and close with \).

　　　　-----Displayed math environments; they open with \[ and close with \].

• Subscripts are typed with _ and superscripts with ^. Subscripts and superscripts should be enclosed in braces, that is typed between { and }.