Installation adds the profile to your phone
Installing an eSIM normally means adding a carrier profile to the device. That profile can exist on the phone before it becomes the line you use for mobile data.
Activation is the event that starts service
Some plans activate when the eSIM first connects to a supported network in the destination. Other products can use a different rule. That difference matters because plan validity is measured from the supplier's activation event, not from when you personally decide the trip has started.
What to check before scanning
Look for the activation wording on the plan or checkout page, keep the QR code available, and avoid deleting the eSIM after installation unless support tells you to. Many profiles are intended for one installation.
If the activation rule is unclear, wait to install until close to departure rather than assuming that installation cannot start validity.
After arrival
Select the travel eSIM for mobile data, enable data roaming on that travel line when required, and confirm that your home SIM is not still selected for roaming data.