FTP, SFTP, and SSH are ways to access files or servers. They sound similar, but they are not the same level of access.
FTP
FTP transfers files, but traditional FTP is not encrypted. Use it only if there is no better option.
SFTP
SFTP transfers files over SSH. It is encrypted and is the better choice for most file-management work.
SSH
SSH gives command-line access. It is powerful, but also easier to misuse. Use it when you need to run commands, manage deployments, or work on a VPS.
Credentials
Create separate users where possible and remove access when it is no longer needed. Avoid sharing your main hosting login for temporary work.
If you only need to upload a theme or edit a file, SFTP is usually enough.
