Get started with example for ESP32 device using Arduino IDE.
Watch exampleYou can install component for Home Assistant from GitHub and control your devices with smartphone or web application. Get component
This service are free, you don't need to pay for use it.
You can compile your code to binary, upload it to relay and device will update on next startup.
Relay does not save any info about your device (state or system info) on DB, it only transfers it from your server to device or to reverse.