There are many exercises and practices intended to produce physical fitness- running, weightlifting, cycling, yoga- but what is going to be helpful to you in meeting your goals?
I just used the word goals- probably out of habit. We live in a culture where everybody is supposed to be setting goals, reaching goals, exceeding goals. In my personal experience- which is nothing to be emulated- goals tend to be things that never happen. My current goal is to stay steadily employed, which may be an unrealistic dream.
In any case, let us first consider what kind of body type is appealing to women. Some like the bodybuilder type, but not many. A few go for the emaciated heroin-addict rock star look. I don’t think any girls like fat guys, except maybe some fat ones.
So you want to be not fat, and somewhat muscular. I recommend a program of weightlifting and muscle-building. Beyond improving physical appearance this will give you a big boost of confidence and a feeling of power. Go to a gym and get signed up with a personal trainer. Get a good one, which is easy because he or she will be in excellent physical condition. It’s a few bucks but it’s money well spent.
That said, I am switching over to running, as I have gotten a bit fat over the last few years. I had a strange and sudden realization a while back- you see fat people at the gym all the time, but never running. That may because fat people don’t run, but I suspect running somehow signals to your body that it needs to be able to move easily, and thus be thin. Being strong doesn’t require you to be thin- a guy can be really strong, but if he doesn’t need to move quick, can also be a big fat slob, e.g. an offensive lineman. So if you are fat you may want to think about running.