In order to get your apps onto your device, you must first download the AppSheet app from your device’s app store. Any subsequent apps you create essentially run through the AppSheet app. You can read more about this deployment model here.
If you are an app creator, it is a good idea to install the AppSheet mobile app on your mobile device even if you won’t be a user of the app. You may want to test your app out on your own device before launching to your users. You can find AppSheet’s app by searching for AppSheet in the iTunes store (for iOS devices) or Google Play store (for Android devices).
When you launch the AppSheet app, it asks you to sign in, after which it starts an App Gallery (itself an app created by AppSheet!). The App Gallery lets you browse and run your apps, apps that have been shared with you, or public samples on your mobile device.
This becomes a convenient mechanism for app creators to test their apps on their own mobile device in the process of building and modifying the app definition, without having to actually install the apps themselves to the homescreen.
You can distribute your app by sending your users (or yourself) an install link by email. Navigate to the Users>Invite Users tab of the app Editor.
Then you'll be able to enter in the email addresses (or full domain) of those you'd like to share the app with.
This is what the email looks like:
When your users click on the link from a mobile device, they are asked to install AppSheet on their device (AppSheet is already available in the app stores).
Installation is easy. Find out more about installation here.