Greetings dear friend @crypto.piotr
What a tricky situation! It is so simple but NOT easy question.
And when faced with a query like this, I think it is best to focus only on the main aspects and ignore small details.
Even if your explanation is not complete, I think it is better than drowning the newbie recipient with so many details that will eventually obscure the crux of the subject.

Let me try:
Imagine a room censored by cameras from every direction and these cameras are broadcasting live to all parts of the world.
You have in this room well-locked boxes (block) made of transparent glass so that anyone anywhere in the world can monitor the contents of these boxes without accessing them.
These boxes are linked together (chain)and each of them has an amount of money.
Each box has two types of keys: the private key and the public key, and each has its own use.

Let me start with the private key:
The private key is the ONLY way that you can own one of these boxes and can access its contents. Anyone who has a copy of the private key to your box can control the money so you MUST be careful with it.
If you want to withdraw your money or transfer it to another box you will need your private key to confirm the withdrawing or transferring process.

Public key:
Assuming that you own one of these boxes (box A) and want to transfer money to another box (box B ), then you need the public key of box B to make that transaction, and after confirming, the money will be transferred from (box A) to (box B) through the links between the boxes, and given that there are cameras in the room anyone can monitor the transfer process.

Now, we have miners:
Think of them as the ones who are responsible for getting all transactions between boxes executed. In exchange for doing so, they take a fee from each transaction process.

Certainly, This approach does NOT cover all the aspects of Blockchain technology, but I think it could introduce the basic description to someone with zero knowledge to get started.

Thank you for sharing your experience :))