What eTravel replaced
Before the system existed, arriving passengers filled out paper arrival and departure cards. The Bureau of Immigration describes eTravel as having abolished those paper cards, and it is run jointly by a group of agencies including immigration, tourism, information and communications technology, quarantine, customs, health, transport, justice and the national privacy commission.
The Bureau of Customs describes the underlying platform as a digital data collection system for travellers and crew arriving in and departing from the Philippines, incorporating its electronic customs baggage and currency declaration interface. In other words, one registration covers what used to be several separate paper forms.
Who needs to do it
All arriving passengers, both Filipino and foreign, including crew members, need to register or update their eTravel information.
Departing passengers generally do not, with specific exceptions: diplomats and their dependents, foreign dignitaries, holders of 9(e) visas, and holders of diplomatic and official or service passports.
If you are arriving in the Philippines as a tourist, that means you register, regardless of nationality and regardless of which airport you land at.
When to register
The window is narrower than people expect. The official guidance is that you may only register within 72 hours prior to your arrival in the Philippines.
That is a real constraint on planning. It rules out completing the registration when you book your flight, and it means the task belongs on your list for the two or three days before departure, alongside checking in for the flight itself.
Free, and only one official site
This is the part worth being firm about. The official site states that eTravel is free. The Bureau of Customs FAQ states that registration is free of charge and does not collect or require any form of online payment, and that etravel.gov.ph is the only official registration website for international inbound travellers. The Bureau of Immigration has separately issued a public statement that registration is free of charge and directs travellers to register only on the government's official website.
Search results for terms like Philippines arrival registration routinely surface third-party sites that charge a fee to complete a free government form. There is no service they can provide that you cannot do yourself in a few minutes, and handing your passport details to an unnecessary intermediary is a poor trade.
What you get, and what to do with it
Registration produces a QR code. The Bureau of Customs guidance describes presenting it before boarding and to quarantine officers on arrival, and the airport's passenger guide treats it as part of the standard arrival process.
Save it somewhere that does not depend on a data connection. A screenshot in your photo gallery, a copy in your email downloaded for offline access, or a printout all work. Arriving at immigration and trying to load a QR code on airport wifi with a queue behind you is an avoidable stress.
What eTravel is not
It is not a visa. Entry eligibility is a separate matter handled by the Bureau of Immigration, and registering for eTravel says nothing about whether your nationality requires a visa or how long you may stay.
It is also not a substitute for the documents an airline may ask for at check-in, such as onward travel or accommodation details. Treat eTravel as one item on the arrival checklist rather than the whole checklist.
A short pre-flight list
Passport valid well beyond your travel dates. eTravel completed within the 72-hour window and saved offline. Entry requirements checked for your own nationality. First-night accommodation confirmed. Do those four and the arrival itself is usually the easy part.