How often should I go to the gym?
You can make faster progress on 5 or 6 days per week, but to make this work needs a well put together training plan, and diet. If not, then training 5 to 6 days can set you back and slow down your results, or lead to injuries. If you want to keep things straight forward, it's better to stick to 3 to 4 days per week. It's going to work across the big picture of fitting into daily life better.
If your goal includes dropping body fat, then you'll have more success including some cardio time too. 3 to 4 x cardio sessions per week is the minimum that help best for most people. 5 or 6 cardio sessions per week can work better, but as the amount of sessions increases, for lean muscle support, then diet becomes much more pivotal. If your goal is lean muscle support, and maximum fat burning, then the diet can definitely become the limiting factor. It takes work to get this right. That's why some people say results are 80% diet, 20% training. As you get further down the road it's more like 90% diet, 10% training.
As far as how often should you train each muscle group each week, depends on how many workouts you can fit in, and your preference. You should always aim to hit each muscle group a minimum of 1 x per week though. Traditional weight training principles are usually based on hitting each muscle group 1 to 2 x per week. This works well. But if you prefer to train muscle groups more, then the results can be similar across many ranges. All the variations have been tried and shown success, there's no hard and fast rules on this one.