OK there are multiple points I need to make for this.
First, is the ever so socially desirable “thigh gap”. A thigh gap does not mean you are sexy or healthy. Although I’m not saying people who do have them aren’t, no body shaming here. It is simply how your bones are arranged in your body. In fact, for a lot of people, it’s impossible unless you are sickly thin. For example, I will never have a thigh gap and I will never strive for one because my body is not built for one. Your legs are not meant to be the same width all the way down. Your thighs are supposed to be bigger than your calves. That is how the human body is built. Not only do you have more muscles in the upper region of your leg, but they are also designed to be larger than your calf muscles to give you stability and power while walking, running, jumping, etc.
Second, six pack. Visible abdominal muscles are more a matter of the amount of fat on your abdomen than simply working them out. Everybody has a six pack - everybody. It’s just making them visible and that is clean eating. You can work your abs all day long, but if you don’t eat healthy, you’ll never see them. Again, you don’t need a six pack in order to be considered sexy or healthy. Although I do understand this one as a goal a lot of people strive for and it is possible for everyone to achieve in a healthy manner.
Third, perkier bottom - squats, lunges, wall sits, any exercise having to do with your boootay. Hiking, stair climbing, walking (especially uphill), stadiums, cycling, etc. All of these focus on your rear end.
Fourth, as for tackling the whole body or focusing on one part of the body a day, that depends on your specific goal. Most should do a total body workout 2-3 times a week for regular strength training, weight-loss training or alternating body composition (specifically circuit training for this one), maintenance, or just trying to stay in shape. For hypertrophy, do super-sets as well. To give your body rest, don’t strength train two days in a row. A split routine, or doing different parts of your body on different days, is for optimal hypertrophy and is usually used with strength athletes and body builders.
** if you came across any names or something I didn’t explain completely through take a look at my FAQ, I explain what super-sets, circuits, split routines are and more.