a berth i think is something for the cargo ships to come alongside stations to dock.

also i was playing reyens mod beta 2.3 or something like that, and he has put docking rings on all the stations so you can dock with the battleships that are in the mod to fly

Berths are those docking stations with the opening doors. They're for small ships.
Moors are those towers and tree-like structures (over docking rings). They're for large ships.
If you give a cap ship the "can_use_berths" property, it will try and dock in the docking bays of stations. It doesn't work, as the ships hit the station and bounce off.
What you can do, though, and this has been discusses with some depth in other threads (because it's not a TRUE solution to the mooring issue), is change any moor_large stations into berth stations in solararch.ini, and give it a radius of 100m or so. This allows cap ships to dock at stations that have large moors (they'll fly toward the moor, and enter the station at ~100m away). You can also do this to one of the medium moors on all stations that don't have a large moor (if you change all the medium moors, you'll never see cargo ships just sitting there in space, docked to a station). This will give capital ships access to all stations in the game, I believe.