Hey the19thbear!
This should be a simple one to fix.
The object picker tool + camera variable will be available when you have the Scene Manager selected (And the camera variable is ‘Instanced exposed’ (via the eye icon next to the variable in the blueprint window)). The picker is represented by the dropper icon next to the variable in the details panel like below, where you can select this button then click over the camera in the scene. Alternatively, you camera should show up in the dropdown list also next to the variable in the details panel.
As for the scene setup, video tutorials are difficult on my end at the moment (hardware/software issues), but I would definitely suggest taking a dive into the example content to see how things work under the hood, along side the documentation tutorials, support email etc to make up for this if you can. Things like adding characters to the scene can be as simple as dragging your character instance from the content browser, but for engine features like the navmesh volume you can checkout the official documentation or search for some videos online to give you the rundown on how to setup and use this feature, which would definitely help.
Hope this helps!