Whenever I add an image to any post the image takes the entire width of that section leaving no place for text and text continues to be shown below the image.

i.e. The width of my 'post box'(or whatever you call it) is 500px(remaining is for the sidebar). If in a post, i place an image of width 200px, the remaining 300 px to the right is plain white. I want to see text there(the article text should be continued from the side and not below the image), can any specific plugin be used for this purpose?
Let me know if you are not able to understand what i'm trying to say.
Thanks in advance.