Upload the unzip file in Wordpress theme folder and activate the theme. Follow the automatic installation and install the "GRIDBY Plugin Bundle" required.
Go to Page -> Add New, and create 1 page (for example: "Home")
Open the "Home" page, in the "Page Attribute Metabox" select the template you want (for example: "Grid + Cover" for demo layout).
Go to Appearance -> Menu, create a new menu, call it "Main" and select "Main Theme Locations" (next add page to the menu).
Repeat Step 4, call the second menu "Footer" and select "Footer Theme Locations" (next add page to the menu).
To set the Grid title and description in Wordpress menu select, Appearence --> Customize click grid and insert your title and desc. After this click save.
To add elements to the grid in Wordpress menu select, Grid -> Add Content (to order the items use attributes order in edit content page).
Set the Home Page: Go to Settings -> Reading -> Front Page click static page and select the "Home" page.
To add buttons in the content editor (tiny MCE) click "Button", insert text and link. To add video from Youtube paste the url of Youtube page in the Video Metabox (post backend page).
To insert Gallery use the standard system of Wordpress. Select in the options of the gallery "Link to media file" to activate the Pop Up System
To change Fonts or Grid Padding go to Apparence --> Customizer.