Hello, Sharon:
As far as I know there is no dedicated command or short-cut key to toggle WiFi whether on Lenovos or in Windows. The usual way to do it is to open Settings and Network and Internet. You can then choose between 'WiFi' or 'Airplane mode' in the menu to the left. 'WiFi' only concerns WiFi, whereas 'Airplane mode' shuts down/turns on all wireless components.
However:
a) If you have an older Lenovo ThinkPad (I have a 9-year-old T61) it may have a physical toggle button on its front. This feature is not available on 'modern' Lenovos, e.g. my 3-year-old Ideapad Y50.
b) Some laptops may feature a small icon on one of the top-row keys (the F-row). The icon looks like a small antenna with radio beams around it. It usually...