Why won't my Microsoft Word program stop indenting each new line, mid-paragraph?

The program I'm using to type up my story is Microsoft Word, 2010. I've been using it a few days now without any trouble, but there's suddenly a problem that I can't fix. Basically, I'll be writing a long paragraph, one that takes multiple lines, and the program keeps indenting as I reach each new line. I try to backspace out of it, to delete that indentation, but all it does is delete my previous "space" and mesh my words into one line with that indentation intact. If anyone knows how to fix this or even why it's happening, I would be incredibly grateful.