{spacing} is about both horizontal and vertical white space, e.g. space between letters or words, or space between paragraphs. For adjusting the space between the lines of a document, use {line-spacing} or -- if your question is specifically about the package of the same name -- {setspace}.
{spacing} is about both horizontal and vertical white space, e.g. space between letters or words, or space between paragraphs.
Examples of spacing commands are \hspace, \vspace, and ~, but there are many more.
For adjusting the space between the lines of a document, use line-spacing.
There's also the setspace package. It provides double spacing and one-half spacing, but also arbitrary spacing which can be restricted to environments. If your question is specifically about this package, use setspace.
