The Lightning App Builder is a point-and-click tool that makes it easy to create 3 different types of page. Home page, App page and Record Page for the Salesforce mobile app and Lightning Experience
How to create a Lightning App builder
Go to the Setup -> Search App Builder in the Quick Find box -> then select Lightning App Builder.
Select Lightning App Builder.
Choose page type
Name your page and if it is record page then find the object
Choose the Header, Subheader, Right Sidebar template on the next screen
Tour the Lightning App Builder
A. The canvas is the area where you build your Lightning Page for desktop and phone. drag and drop components from the left side bar (see B and C) onto the canvas in the center
B. Standard Lightning components provided by Salesforce with Lightning App Builder.
C. Custom Lightning components created by you, built by developer or installed from AppExchange packages.
D. The preview picklist changes the form factor of the canvas so you can get an idea of how your page will display on different devices.
E. Controls for the App Builder. Save the current definition of your app. Activate adds your app the the Saleforce1 Mobile navigation. Back To Setup exits Lightning App Builder and returns you to the list of Lightning Apps.
F. Properties for the currently selected item. This can either be for the page itself, in which case the title will indicate Page. Otherwise you can set properties for individual components. In this instance the title will indicate Page > [SelectedComponent].
G. Selected publisher actions for this Page. Only global publisher actions are allowed in a Lightning App Builder App. Actions must be defined before you use them in your app by going to Setup > Create > Global Actions > Actions.