Connect a suitable cable from the external hard drive to the eSATA port on the system’s backplate. Note that in general, for use with large video files the hard drive should be formatted using the NTSF file system (the FAT file system chokes on exported files exceeding 4 Gigabytes, as will often be the case).
The eSATA port supports transfer speeds that are fast enough for live recording to suitable external media. USB ports should not be used for recording, but may be useful for transferring files to and from the system (it is always best to import media for use in live sessions).