The normal Reprint action sends the print job to a Windows printer, this means it is queued if the printer is unavailable but does add some ovehead if you are reprinting very large documents.
The Direct Reprint action sends the print job directly to a network attached printer. The printer must support TCP/IP and either the LPR/LPD protocol or AppSocket (port 9100).
During printing the action will block until the whole document is spooled to the printer, if the printer is not connected then the action will fail, for this reason the Direct Reprint would normally be a child of a Failover with an alternative Reprint to queue the document.
If you are using LPR/LPD then you will need to specify the queue name on the printer, your printer manufacturer will be able to tell you what to use, commonly it will be PR1, PR2, etc.
If you are using AppSocket then you will need to specify the port, this will typically be 9100, 9101, etc.