Chefs and the cooks who know their way around a kitchen (or a grill) know how meat feels when it's raw and when it's cooked. The only way to learn this is to basically poke the steaks at different stages of cooking. Raw meat is almost squishy, rare meat is quite soft, medium rare meat resists your poking a bit, and medium meat springs back. Once meat feels firm, it's at least well done, if not completely overdone. Gently press a finger onto your steaks—being careful not to burn yourself—to teach yourself the difference.
Brush your grill grates after every use (inspect for wire brush bristles before cooking), and thoroughly clean them every couple of months, depending on grill usage. And twice a year, you should give your grill a thorough cleaning, which helps it cook better and last longer. The basic process is the same for gas or charcoal grills; charcoal grills just have fewer parts.