An eSIM is a SIM embedded in your device, so you never have to deal with physical SIMs again! They're a new technology, so not all phone support them, but this article will tell you how to check.
How to Check If Your Phone Supports eSIM
For iPhone:
Open Settings and tap on Cellular or Mobile Data.
Look for Add eSIM—that means your iPhone supports eSIM!
For Android Device:
Head to Settings and find Network & Internet or Connections.
Search for SIM manager.
Then look for Add eSIM—that means your iPhone supports eSIM!
For All devices:
DIAL *#06# and press the call button.
If your device is eSIM-compatible, you should be able to view your device's eSIM unique identification number (EID).
You may visit this link to verify your phone's eSIM compatibility.