Land based VOR/DME equipment doesn't have the range to transmit over oceans, therefore, points in the ocean at a given longitude and latitude are given names, airways are projected between them and hence you have a point to point oceanic navigation. On board the aircraft, the inertial guidance system, which you program in prior to leaving the gate with it's position (exact long/lat) and enroute navigation points (VOR/DME/ADF etc) along with the position fixes, which someone with no other job gives silly names to allows you to plot your course accurately over oceans.
So long as you know where a navigation point is (with long/lat) there is no real way of getting lost unless your onboard equipment fails or you programmed it in incorrectly. Most FMC's (onboard computers) are preprogrammed by the navigation department with the relevant data, so your main task is to set the start co-ordinates accurately, then enter the planned route, your FMC will tell you if there is a route discontinuity, this is where cross checking with the other crew member comes into it's own. One enters the info, and the other cross checks it.
Communication is via HF over oceans, and over some land areas as well. It is a high frequency signal bounced off the atmosphere to a large attenna array on the ground. Sounds crappy when you use it, but an essential part of radio and communication. Sometimes when certain atmospheric conditions prevail, signal and reception is poor, which then as an unwritten rule, other aircraft act as a radio relay. You talk to the other aircraft and they use their better signal to relay the information. Over land it tends to be better, as VHF has good coverage, also the use of radio repeaters is used to enhance reception and transmission.
Hope this helps