How to use 事?

Hello everyone, I need your help 🥲
In japanese, people often use 事(こと) in the sentences, but I don’t understand how it works.
I can understand if it’s used for abstract things for example in this phrase:

昨日の事は、何も覚えてない。

Here it’s simple and easy.
But I see this 事 uses for other things, for example in this one:

お金を大切にすること

Can you explain this to me please? 🙏

I will study the argument soon on my book but I can’t stand this “not understanding” in the meanwhile 🙈

手伝ってください！