create a submenu

Hi guys,

I am trying to create a submenu like the one Gavickpro used
on their website but unfortunately I cannot do it so I need
your helps please. Thank you!

But what steps have you made and why there is a problem?
You have posted a link from out site that is custom made template.

I have tried to create a submenu but when i cliqued on the button on im getting the following answe (please the screenshot I attached to this message.) Thank you!

You should edit menu from the backend not the frontend.