How to Turn ON the main menu on Mobile ?

Hi,
I am setting up a small community website i see everything perfect on desktop version
but as soon as I see it on my mobile there is no Main Menu, well I know I can use
Side Bar but i want to use it for something else so please help me and tell me how I
can get a Main menu may be like a drop down or something like that goes with Mobiles

guide me on how to get Main Menu on Mobiles and Tablet right now I see none

Sorry to request you this but right now I have attached my website Mobile Screenshot
but I don’t want to keep it in my post in future as an backup on your website
once the problem is resolved you can delete my question of just delete is image
please this is a humble request