Visitors to the UK from a host of locations including Hong Kong and Macao now face a different process at the border, with the implementation of the new Electronic Travel Authorisation (ETA) scheme. 

ETA aims to improve the pre-arrival screening of people coming to the UK without a visa, either as a visitor staying for up to six months, or on a temporary creative worker concession for up to three months. 

The idea is to screen and assess potential travelers more effectively – although it should be noted that if you are rejected for an ETA you're not necessarily banned from entering the UK: you would, however, need to apply for a visa.

The ETA is automatically linked to the applicant's passport and allows the holder to enter the UK multiple times for two years after it is granted. All travelers, including children and babies, will need their own ETA – but it is possible to apply on behalf of other people, such as your relatives. 

You can apply using the ETA App (available via App Store or Google Play), or via an online form. Either way, there is an application fee of £10 (currently $12.36). You will answer a set of questions about your suitability, but you do not need to enter your travel details.

You will need your physical passport (not a photocopy or digital version); a credit card, debit card, Google Pay or Apple Pay; access to emails; and you will need to upload photographs of each applicant and their passport. 

For more guidance, see the UK government's site.