To add a section of the Avik site to the main menu, with effect to scroll, you need to proceed like this:
From the menu item choose Add Items
Choose Custom Links and in the url, insert the entry in the section preceded by the #
In the text link, enter the title you want to appear in the menu.

List of sections:

AVIK PRO

#banner
#slider
#focuses
#cards
#parallax
#about
#portfolio
#testimonials
#experience
#stats
#services
#team
#contact
#blog

AVIK FREE

#who-we-are
#services
#portfolio
#avik-blog
#contact

See Portfolio Section