Jetbrains changed the toolbars in IntelliJ 13.
The Navigate Back & Forward arrows, shown here, used to be in the top toolbar and easily clickable.
I am using Idea 13 and my toolbar already has these buttons:
The icon groups are:
file | undo/redo | cut/copy/paste | font size | back/forward | compile/run | vcs | config | help | jira | tasks
You should be looking at the back/forward buttons in the 5th group.
If you want to make the toolbar visible, it's one of the checkable options on the view menu.