95 Nissan won't turn over, battary is good, actng

First you need to load test the battery you can show 12 volts on the battery and it will turn lights on and all that fun stuff but once you put a load on it like a starter the voltage will drop out... first check the battery while trying to start the car see what the voltage goes down to when you turn the key to the start possition just don't hold it there for more than 15 seconds... and then comment back and we will go from there...

CHECK FOR LOOSE IGNITION SWITCH BEHIND THE KEY YOU MAY HAVE TO REMOVE THE SCREWWS HOLDING THE STERRING COLUMN COVER ON, ALSO OTHER THINGS IT COULD BE WOULD BE YOUR NEUTRAL SAFETY SWITCH OR THE STARTER RELAY AND FINALLY THE STARTER? YOU WOULD NEED A TEST LIGHT TO DIAGNOSIS? ONE THING YOU COULD TYR IS REMOVING FUSE/RELAY COVER UNDER HOOD AND SWAPPING THE STARTER RELAY WITH A SIMILAR ONE IN THE BOX ? IF IT STARTS THEN THE RELAY IS BAD ? GOOD LUCK