As you are a girl looking for a summer body, you probably aren't looking for upper body strength so just do ab work outs. The best ab workouts in my opinion are leg raises and planking. Both can easily be done at home, just use your bed to hold onto when you are doing leg raises. Don't be discouraged if you have difficulty, it will get easier the more you do it.

Do 20 leg raises, rest for 15 secs, do 40 bicycles where you are on your back doing the bicycle motion (20 on each leg). Rest for another 15 secs. Plank for 30 secs, rest 20 secs, then do 20 situps. Take your time with them, do them properly or else nothing will happen. Take a 5min break and then repeat. If you wake up the next day and your stomach feels tight/sore then you were doing everything right.

And yea I forgot to say at the start but this is assuming abs are part of your "summer body" and you are already fairly slim just with abit of excess fat around your belly. If not then definitely do cardo with running/diets the others have suggested to lose some body fat and then use ab workouts to take it further.