The Off Canvas Builder is found at Avada > Off Canvas, from the WordPress sidebar, or from the menu on the Avada Dashboard. This is where you create and manage all your Off Canvas creations.
To get started, simply give your new Off Canvas a name, and click on Create New Off Canvas. Depending on whether you have Avada Builder Auto Activation turned on or not in the Avada Builder Options (Avada Dasboard > Options > Builder Options) you will be taken directly to the Avada Builder, or alternatively, the WordPress editor. In that case, simply click on your choice of builder, either Avada Builder, or Avada Live to start building.
In either case, the first thing you see is a choice to either Add a Container and start building from scratch, or to open Avada Studio. and import a prebuilt Off Canvas.
Avada Studio is a great place to start. There is a range of prebuilt Off Canvas items here you can use, and these come fully designed and pre-configured. Simply select the one you want and it will be imported ready for you to customize. This is a great way for you to familiarize yourself with the different types of Off Canvases that can be made, and also how to configure them.
If you choose instead to build an Off Canvas from scratch, simply select your starting Container/Column combination and get building. You have the full range of Avada Design Elements to build with.