Subscribers to your newsletter are called Contacts in Keila.
You can see a list of all contacts on the Contacts page which is accessible from the main menu:
If you already have an existing list of subscribers that you want to import into Keila, you can do so by clicking on Import Contacts on the Contacts page.
Keila can import contacts from CSV files. Make sure to follow the instructions on the Import Contacts page to ensure your file is correctly formatted will be imported successfully.