Why can't I insert a legend?

[MINZHIYE]

Why can't I use the legend? 

[FC_Basson · Accepted solution]

You are probably in Data View and need to switch to Layout View

Displaying maps in data view and layout view—Help | ArcGIS for Desktop 

[MINZHIYE]

Thank you, very helpful!

[FC_Basson]

Great.  Please mark the question as answered if it resolved your issue.