To connect to an SFTP server you need four things: the host, the port (22 by default), a username, and either a password or an SSH private key. Enter them into an SFTP client and connect.
Run sftp username@host to connect on the default port, or sftp -P 2222 username@host for a custom port. You will be prompted for your password, or your SSH key will be used automatically if it is loaded.
FlowSetu's browser-based SFTP client does all of this without installing anything - useful on locked-down or shared machines.
Check the port, confirm the host is reachable and not blocked by a firewall, and verify your username and password or key. An SFTP connection tester will show the exact error the server returns.
Try the free online SFTP client — connect to any SFTP server from your browser, no install required.