Select the type tool (Cmd+T on a Mac, Ctrl+T on Windows). Instead of clicking to create point type, drag to create paragraph type with bounding rectangles.
To convert your already-entered point type to paragraph type, select the type tool, right-click on your type layer in the comp viewer, then choose Convert to Paragraph Type. (It will contain line breaks that you'll have to remove for proper flow.) When you click in the paragraph type with the type tool, you'll see (and can adjust) the paragraph boundaries.
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events