Over heated, no coolant..

I drove out of town today about 73 (1h 15min) miles and truck was fine. I arrive at my destination for my job and at the end of the day I start to drive home, upon waiting at the gas station while talking on my phone ( illegal to talk on phone while driving ) my truck over heated. I shut it off and let it cool for about 30 minutes, and turned the heater on full blast and started to head home half way home the service engine light came on. The temp gauge was at the middle of C and H like normal. I get home and let the truck cool for a few hours and pop the radiator cap and check the reservoir. To my surprise its completely empty, and you can see down into the radiator. I added some coolant to the reservoir maximum level and drove it around town and it started to climb abit again and then level off. I haven't checked the level again as I am letting it cool down.

Have I messed anything up running it without any coolant? It never reached H when I was driving it tonight. However I am concerned how I have absolutely zero coolant and I didn't see any traces off it on the ground or around the engine..

Do I add coolant to the radiator and then the reservoir? I always though to fill the reservoir up and let it pump coolant and add more if needed.

02 Nissan Frontier Crew Cab
80,000 Miles