This is typically due to the Text format selection. To wrap text around an object such as an image, media player, or table, a float must be applied. For a float to work, the Text format on the content submission form must be set to Full HTML.
If you happen to notice a pink colored background behind your content and it is not part of your site's theme, this is most likely due to the state your content is in. Draft content, content that is in process and only viewed by logged in site members, will display with a pale pink background.