First and foremost, if you have not already done so, create a Google account. Since the Android operating system was created by Alphabet, you will be able to take advantage of all their services: Gmail, YouTube, Google Drive, or even Google Calendar and Contacts. Your data will be automatically synchronised between your various connected devices.
NB: Create this account carefully and remember to keep a note of your address and password. If you lose your phone, you can recover your contacts and even geo-locate the device directly via your computer.