The "Legend" is the "box" found on both the "page" created by eeSchema and the "page" created by PCBnew.
It is just a traditional element… for good reasons… of the design process.
In the lower right hand corner you will find some important information about the drawing. What appears here is something I need to write more about for you.
One the I'll mention now: While I don't, in general, like putting version IDs in filenames, you will find in KiCad that the practice pays you a dividend: Notice that the filename the drawing was done from/ saved in appears in the legend text. Put a version ID in the filename, and you put it on the drawing!
(This entry needs expanding! If you particularly want THIS expanded, write and cite "Page co1leg")