An alias is a personal identifier. This is a marker that allows you to send personalized offers, and trigger notifications. How are aliases assigned to subscribers? When a push subscriber visits the website and logs in there, their personal identifier from the website will be stored in the push system. It can be their email address, login, token, etc. After that, the subscriber can be identified and you can send them push notifications individually. 

A subscriber is assigned one alias, but can also have many tags.

Using REST API, you can perform the automated distribution of transactional messages (payment reminders, order confirmations, etc.).