Chris
5320N is a naming convention for latlong waypoints used on the North Atlantic. It fits in with the usual 5-character format (like REFSO, etc).
5320N is 53 deg North, 20 deg West ( the West is assumed, hence 5320N)
These waypoints are all stored in the FMC/FMGC database, so you enter them as 5320N giving less chance of entry error etc.
An Atlantic routing may be from domestic routing to xxxxx (Oceanic entry point) to 5315N, 5520N, 5730N, 5840N, 5750N, 5660N, yyyyy (Oceanic exit point) then domestic routing to destination.
The 747-400's didn't have CPDLC when I retired in 2009, but basically it replaces the need for HF reports/requests every 10 degrees with automated data reports.