Short answer
Open light-ark-church.com and tap the main button on the home page: "Start talking now · Free · In your browser." Nothing to install. If you like, you can also add Light Ark to your phone's home screen from light-ark-church.com/download, which takes about 30 seconds. Light Ark is free and is for adults 18 and older.
Light Ark uses one account across the web and the installed version, so once you sign in, your memories and data follow you when you switch devices. You'll then see a sign-in page: sign in, or tap "Skip sign-in, just explore." The pastor you talk to is an AI, clearly disclosed. When you begin using it, you are asked for your birth year and month; the privacy policy says this is used solely for the 18+ age check and as consent-record evidence.
Optional home-screen steps, from the download page. On iPhone or iPad, use Safari: tap the Share button, find "Add to Home Screen," then tap "Add." On Android, use Chrome: tap the menu button, tap "Add to Home Screen," then "Add" or "Install." Or just keep using it in your browser.