Hi, cloud-init will by default create a user named "centos" and add your chosen SSH public key to the authorized_keys file. The account will also have sudo access without the use of a password.
However, we recommend that you look into defining a user-data file to inject during bootup, to set various settings during launch.
Doing this will let you add your own user instead of the default, it can help you patch your system to ensure that packages and kernels are recent, and also add the hostname to /etc/hosts. And set the correct timezone. Etc.