On Android the option names differ between manufacturers, but the logic is the same: you add a new mobile network from a QR code.
Samsung Galaxy
- Settings > Connections > SIM manager.
- Tap Add eSIM, then Scan carrier QR code.
- Scan the code and wait for the profile to download.
Google Pixel
- Settings > Network & internet > SIMs.
- Tap Add eSIM or the plus next to the list.
- Scan the QR code.
Xiaomi
- Settings > SIM cards & mobile networks.
- Choose Add eSIM and scan the code.
After installing
Give the profile a label you will recognise. Then in the same menu:
- set mobile data to the eSIM profile (only once you arrive),
- leave calls and SMS on your own SIM,
- turn on data roaming for the eSIM line.
If there is no eSIM option
Then the device either has no eSIM or is a market variant without one, such as some China models. Check your model on the device checker before you buy.