I can not export my photos there's no export tab on my screen

If you can't see the Export button, you have probably hidden the left side panel. Press F7 (or Tab) to get it back.

F5 shows/hides the Module picker, F6 shows/hides the Film strip, F7 and F8 show/hide the left and right side panels, Tab shows/hides both side panels. You can also click the little gray arrows at the sides of the screen to show/hide panels, right click the arrows for options.

There is no Export button in Develop, but you can use keyboard shortcut (Ctrl+Shift+E) to export, or go File > Export.