Why would your cells need enzymes at all?
Your body is full of chemical reactions that would be way too slow on their own. Enzymes let your cells run those reactions fast enough to keep you alive, and they also help control when, where, and how quickly each reaction happens.
When a reaction needs an energy boost before it can start, that starting barrier is called activation energy.
An enzyme is a biological catalyst, which means it speeds up a reaction in living things by cutting down the activation energy needed to get started.
Because that barrier is lowered, reactions your cells depend on can happen at a useful rate instead of dragging on.
A surprising part is that the enzyme itself is not used up. After helping one reaction happen, it can do the same job again, so your cells can keep reusing the same enzyme molecules.
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