Grill Cutout Kit vs a  Grill Platform kit. 

A Grill Cutout Kit creates the opening for the grill to slide into

A Grill Platfrom Kit creates a shelf for the grill to sit on.

Most grills are counter top supported and do not require a platform.  Brands include: Fire Magic, Bull, BBQ COACH, Blaze...

Some grills require both a grill cutout kit + a Grill plat form kit

Brands include: DCS, LYNX, VIKING...

Check your grill owner manual or ask the dealer who sold it to you.