To turn on the Word Wrap feature, go to View > Toggle Word Wrap or click the Edit Display icon in the Code Editor toolbar (it's the second-to-last one on the right) and select Toggle Word Wrap.

You can also set the program preferences to keep this feature on by default. To do this, go to Tools > Preferences > General tab. Under the Miscellaneous heading on the lower right-hand side, put a checkmark next to where it says "Word Wrap on by default."