Actually, their naming makes sense. They have way too many trim levels, but that's a different story.
In the sports cars, you have the three main models. The 911 Carrera, the Cayman, and the Boxster. Each are available in base, S, and GTS trim. On the 911 these can all be had in two or all-wheel drive (appending a 4 to the model name) and in coupe, cabrio, or targa body styles.
Then, there are a couple special versions. There's the 911 Turbo, which is only all-wheel drive and is their top of the line GT car. Their more track-focused somewhat stripped down drivers car versions take on the sports car race class naming structure of GT1 (which was a 911-based hyper car), GT2 (a turbocharged 911 variant), GT3 (a normally aspirated 911 variant, which has an even more extreme RS package available and a competition only RSR variant), and now the GT4 (Cayman based).