If I got you correct, You would like to know about where
Top primary menu is written.
So answer is simple, it is the part of the back end.You need to
login to your admin dashboard.
login , Go to
Appearance > Menus. When you go here, you will find below screen:
In above pic, you can find
Menu Name. Here you need to create Menu first. Give any name. I have given My Menu.
After giving any name, you can see
Create Menu button. Hit that button to create Menu. So now will see following screen.
As you can see in above picture, there is two tab now.Second tab is
Manage Locations. When you click on that tab, you will see above to text.See below picture:
So basically, these name is for the locations of the menu where you can decide which menu should appear in which location.