Two ways to get a travel eSIM onto your phone exist, and you'll usually only meet one of them, depending on how you bought your plan and which phone you're holding. Neither is more "official" than the other - they're just two doors into the same room.
The QR code route
This is the older, more universal method, and it works on essentially every eSIM-capable phone regardless of brand. Buy a plan, and you're emailed (or shown, on the confirmation screen) a square barcode. Open your phone's SIM settings, choose "scan QR code," and point the camera at it - printed, on another screen, or the same screen if you're clever about angles. Your phone reads it once, downloads the profile, and the code has done its job.
The catch is in that word "once." A QR code for an eSIM is typically single-use: after it's redeemed, scanning it again on a second device won't add the plan there too. If you're buying for a travelling companion, they need their own code, not a photo of yours.
The one-tap route
Newer, and only available when you're signed in on the same phone you're installing to. Instead of a code to scan, you'll see a button - "Install this eSIM" or similar - appear directly in your phone's settings or the account page itself, because your phone and the account are already talking to each other. Tap it, confirm, done. No camera, no code, no risk of scanning someone else's screen by mistake.