Okay, so you know how sometimes you might give up chocolate or candy for a little while, like during Lent? Well, fasting in the Catholic Church is kind of like that but instead of just giving up a type of food, you don't eat any food at all (except for a little bit) for a certain amount of time.
Usually, Catholics fast on Ash Wednesday and Good Friday, which are special days in the church calendar. During those days, you can only eat one full meal and two smaller meals that together aren't as big as the one full meal. But don't worry, you can still drink water and other liquids like juice or milk! The idea is that while you're fasting, you're supposed to be thinking about your relationship with God and being more prayerful.
Abstinence, on the other hand, is when you don't eat meat (like beef or chicken) on certain days. This is also a way of showing your dedication to God and remembering the sacrifice he made for us. Catholics are required to abstain from meat on Fridays during Lent, but it's also encouraged on other Fridays throughout the year.
So basically, fasting and abstinence are ways for Catholics to show their devotion to God and remind themselves of his love and sacrifice for us. It's kind of like when you give up something you like as a way of showing your love for someone else, like when you share your toys with your little brother or sister.