Abstention means not doing something that you think you could do. It's kind of like staying on the sidelines during a game instead of actually playing with the other kids.
For example, imagine you and your friends are going to eat candy. If you decide that you don't want any candy right now, even though you could have some, that's abstaining. You're choosing not to do something that you have the option to do.
People might abstain for all sorts of reasons. They might think something is bad for them, or they might think that it's better to wait for a later time. Sometimes, people might even abstain from voting in an election, which means they don't choose any of the candidates. It's sort of like not picking a candy flavor when you were asked to choose your favorite.
To abstain is a choice, and no one can make you do or not do something. It's just like saying "no thanks!" when someone is offering something to you. You can always choose to abstain from something if you think it's better that way.