I just started so which exercises I should do first as a beginner and what a exercises should I do to have a bikini body by this summer
Most of the bikini body girls I know lift weights and use the machines at the gym. They also do HITT cardio and plyometric workouts. Most importantly they eat a well balanced diet full of nutrient rich food and leave out all if the junk. Also, when people say light weight make sure it's challenging or you won't get as much definition and tone. If you aren't sweating, you aren't working hard enough.
As a beginner i suggest you start with a low impact exercises you can try lifting weight about 1 to 1.5 kg. Do simple step you'll see you getting lighter and stronger. Watch your food intake cut off sugar and high calorie food. Good luck