In the box you will find a extender, be sure to use the extender as it helps to give you a better WiFi signal.
Use plug in box to connect to an outlet, do not plug USB into TV.
Once connected may be promoted to connect to WiFi. Click on Circle on left and log in with Amazon log in (same one used for shopping on Amazon). If need to create an account, on phone or computer create free account at amazon.com/account
To see all Applications I have installed:
Click Home button on remote - select Settings - 
Applications - Manage Installed Applications (Any Application you Launch from here will now be on the Amazon Home Screen under Recent Apps)
To see all Addons inside of Kodi: Click Addons on the left and then Video Addons on the left
If any Applications prompts you for an update be sure to install the update. For Applications that you use most often be sure to clear cache to keep things moving smoothly.
To Clear Cache for an Application:
To Move An Application to the Amazon Home Screen:
How to install and use Downloader: