Going to the gym doesn't work. When you're at the gym you tend to move from station to station only ever challenging one set of muscles at a time and doing cardio then weights. It would take you years to get fit that way. Plus it's so easy to stay within your comfort zone. Classes are better because you tend to try and keep up with the class so you will push yourself harder.
To lose weight and increase your fitness and strength you need to really push yourself and push more than one muscle group at a time.
I've been trying to get fit recently. I've noticed a massive difference in just one month using a fitness bootcamp and interval training. The workouts we do in Bootcamp are high intensity interval training similar to the ones on this site It's really hard. But it needs to be to work. If I tried one of those workouts when I first started, last month, then I would probably only manage one or two reps each set, but it's enough to begin with and will get your heart rate pumping and challenge your muscles which is what you need to do to burn calories.
The interval training I do at home between bootcamp sessions. I use couch to 5k and either run with the dogs or do it on the cross trainer. There's no point trying to push yourself to the max for a full 30 minutes, you'd only manage a minute or two, couch to 5 k builds you up slowly, while pushing you enough to increase your fitness.
30 Day Shred is also great and would be much better than joining a gym.
I'm 5 weeks into my new fitness plan and this week have to try and eat more because I lost 8lb last week, even though I binged at the weekend. I want to lose weight slowly enough for it to be maintainable and healthy.
For my diet I try and lower carbs, but I'm not manic about it. If I fancy a sarnie for lunch I'll have one but then I'll have no carbs at dinner time. I try and fresh, whole foods and have protein with each meal. I don't count calories ir points or anything, there is no need to if you're eating well and exercising.
I try and exercise for about 1 hour a day. Today I had bootcamp, which is my hour. Tomorrow I will probably do either one of those vids I've just linked to or 30 Day Shred and couch25k.
Water is essential. Loads of it. I carry a sports bottle and sip throughout the day. When your body breaks down fat for energy it leaves toxins behind which need to be flushed out. The more hydrated your body is the better it will be able to break down the fat stores.
Good luck. The hardest thing is getting started. I still now sit and procrastinate thinking I'll workout just after this coffee/load of washin/after Corrie etc. Once I get going I enjoy and you feel so much better once you've done it.
The first week is the hardest. You'll feel sore, but don't let that stop you. Work through it as best you can. The soreness stops after about a week.