Most likely, your fast will start right after an early dinner (around 6 pm), so the first thing you'll miss is light snacking some people indulge in before bed time.
When you get up in the morning — the only thing you'll be allowed to have is a cup of coffee/tea. If you're doing a 16 hour fast, you'll be at lunch in no time, and you can resume eating as normal.
But if you go beyond 16 hours, things start to get interesting. As your body depletes the glycogen stores in liver and shifts to ketosis (more on this in the next post), practitioners report getting a sensation of mental clarity (whatever that means — you'll have to try it to experience it), and an absence of hunger. You'll find that you're much more focussed at work, and may even feel a little colder than usual!
Remember: drink plenty of water. A lot of water that our body needs comes from the food we eat. In the absence of that, it's critical that you drink a lot more water than you are used to drinking. Not doing so will result in headaches. Also, I recommend adding in a little sprinkle of salt to water to replenish the electrolytes that you otherwise get from your food.
Before breaking your fast, people generally recommend drinking some water since your stomach might have shrunk a bit over the past 16/36 hours. Eat slowly, and avoid foods that are hard to digest like beans, legumes. A lot of people like to stick to a keto diet (high fat, low carb, low protein), and like to continue the ketosis that the fast puts them in. Again, this is dependent on your goals, and a lot of benefits of fasting extend beyond weight loss. We'll explore them soon.