Formatting Images within Post (how to add padding)

Hello. I need help. I’ve tried several themes in WordPress and I continue to have the same problem. Namely, when I upload and insert a picture in a message post, select left alignment from the drop down menu, The text of the post begins at the very edge of the picture. I know I need to change the padding for that but have no idea how.

Am I looking for this info in the Style sheet or some other place?

What area of the style sheet should it be in?

Any help would be appreciated! It’s strange too because I didn’t have this problem when WordPress hosted. But now that I have it hosted on Yahoo, with my own domain name, this has become an issue.