You can log in to a Windows ECS using either VNC or MSTSC provided on the management console.
Figure 1 Windows ECS login modes

To log in to a key-pair-authenticated ECS, use the password obtaining function provided by the management console to decrypt the key file and obtain a password.
For details, see Obtaining the Password for Logging In to a Windows ECS.
For details, see Logging In to a Windows ECS Using VNC.
For details, see Logging In to a Windows ECS from a Windows Server.
The method for logging in to an ECS varies depending on the login authentication methods configured during ECS creation.
Figure 2 Linux ECS login modes

For instructions about how to log in to a Linux ECS using an SSH key, see Logging In to a Linux ECS Using an SSH Key Pair.
If you want to log in to an ECS using VNC provided on the management console, log in to the ECS using an SSH key, configure the login password, and use the password for login.
For details about how to log in to the ECS using VNC, see Logging In to a Linux ECS Using VNC.
For details, see Logging In to a Linux ECS Using an SSH Password.
For details, see Scenarios and Disk Partitions.