It is to left align elements on a page. The only parameter is the content to be aligned. See also Template:Align for more options and flexibility.

With no input arguments, it saves typing the following text (in a table):

style="text-align:left"|

To use, type {{left}} at the start of the table cell. It will leave Category:Pages using left with no arguments.

With an input argument, it saves typing:

<div style="float:left;">...</div>

To use, type {{left|content}} to align contents.

{| class="wikitable" style="width:30em; text-align:center"
!colspan="4"| Header text
|-
| {{Left}} Content1A <br/> Content1B || Content2
|}

Header text
Content1A
Content1B
Content2

{| class="wikitable" style="width:30em; text-align:center"
!colspan="4"| Header text
|-
| {{Left|Content1A}} <br/> Content1B || Content2
|}

Header text
Content1A

Content1B
Content2