Permalinks Problem

Help!!

I am trying to create permalinks that look like this: http://www.parentingwithpleasure.com/postname like I have on my current site, raisingsmallsouls.com, for example: http://www.raisingsmallsouls.com/everything-versus-something/

Under “permalinks” I put this into the “custom” field: /%postname%/ – and my entite http://www.parentingwithpleasure.com site got messed up!

However, I was told to change my htaccess files- what are those and how do I find them and do that?

Please help, thanks!!!