Fasting is like exercise. It is a way in which we learn self-control and practice saying no to things, in order to help us do the same for more serious reasons.
Fasting is a bit like a kind of retreat in a barren land. In the normal course of a day, we are so busy and so many things happen, we don't even see where the devil is tempting us. Were we a bit gluttonous at dinner? Did we look on that person with lust? We we greedy a bit in a business transaction? Often by the time we have asked the question, it is done, or we don't think of it at all.
When we fast we take as many of these distractions out as possible, and come out of the jungle of our everyday life into the barren land. We refrain from rich foods, from distracting leisure activities, from sex, parties, etc, and devote ourselves to prayer. It suddenly becomes very clear where we are being tempted, and we can face those temptations directly.
You can learn a lot from this, but it can also be scary and even dangerous.
I'd suggest that to start fasting the best thing would be to begin with something small, maybe fasting meals one day a week plus some extra devotion to prayer that day, and give whatever $ you save on the food to charity. (So, you could have just one plain meal in the day, or give up all animal products, in accordance always with any health issues.) Have a plan, be regular, and don't attempt anything too hard.
But ideally you should do this under direction of an experienced pastor or priest.