I would say the best exercises to get abs are crunches that are simple and easy to do anywhere are crunches and planks. However, the most important thing to do would be eat healthy and do exercise on a regular basis. Cut out fats and replace carbs with proteins. The very least you can do eating wise would be to eat small portions of the unhealthy stuff and exercise moderately. However, a person really wants abs you have to fully commit to healthy eating and exercise to get them then maintain it.
I AM NO EXPERT but this is my advice. Just make sure not to overdo anything because that won't help you at all.