Install on Android
Menu names vary by brand. These are for Samsung and Google Pixel; others are similar.
Samsung
Settings → Connections → SIM manager → Add eSIM → Scan QR code.
Scan the code on your eSIM page (open it on another screen).
Google Pixel
Settings → Network & internet → SIMs → Add SIM → Download a SIM instead?
Scan the code on your eSIM page.
Can't scan?
Choose "Enter code manually" and paste the full activation string from your eSIM page (it starts with LPA:1$).
When you land
Turn on Roaming for the new eSIM.
Set it as the SIM for mobile data.
When asked to name the new eSIM, call it Travel, so you can tell it from your home SIM.
Rename it later. Samsung: Settings → Connections → SIM manager → tap the eSIM. Pixel: Settings → Network & internet → SIMs → tap the eSIM → edit the name.