SCP (or secure copy) is a widely available and simple-to-use command-line utility that allows you to copy files and directories between two locations securely. It relies on ssh, so when you have ssh access to any server you can easily upload/download files to/from this server.
Uploading files
scp file-to-upload.txt [email protected]:/target/remote/directory
Downloading files
scp [email protected]:/target/remote/directory/file-to-download.txt ./
Flags and options
-P - specifies the remote host ssh port when it's different than 22;
-p - preserves files modification and access times;
-q - use this option if you want to suppress the progress meter and non-error messages;
-C - this option forces scp to compress the data as it is sent to the destination machine.
-r - This option tells scp to copy directories recursively (yes, you can copy directories also).
Also, you can use -i flag to specify a key file for the ssh connection:
scp -i /path/to/id_rsa file-to-upload.txt [email protected]:/target/remote/directory