In wordpress.com blog posts, if you add a few spaces to the beginning of a line, when you publish the post, the application removes those spaces. How can I add spaces before the first word of a line?
Generally, one should not "add spaces at the beginning of a line"; this is something to be left in the age of typewriters. But if this is exactly what you need, then switch to the HTML mode of the editor and put
(as many times as you want) at the beginning of a line. Be careful not to switch to the Visual mode of the editor after that, which may remove this HTML code.
That said, what you probably want to do is to indent paragraphs in your post. This can be done with a style: in HTML mode, put the line
<div style="text-indent: 1em;">
at the beginning, and
at the very end of the post. The number 1 can be made smaller or larger, as you prefer: 0.75, 1.4, etc.