These variants of mouse-1 select entire words or lines at a time. Emacs activates the region around the selected text, which is also copied to the kill ring.
Select the text around the word which you click on.
Double-clicking on a character with symbol syntax (such as underscore, in C mode) selects the symbol surrounding that character. Double-clicking on a character with open- or close-parenthesis syntax selects the parenthetical grouping which that character starts or ends. Double-clicking on a character with string-delimiter syntax (such as a single-quote or double-quote in C) selects the string constant (Emacs uses heuristics to figure out whether that character is the beginning or the end of it).
Select the text you drag across, in the form of whole words.
Select the line you click on.
Select the text you drag across, in the form of whole lines.