I've used the word "pronounce" to indicate the pronunciation of words. However, does it also have the same meaning as "declare?"

What does the word "extra" mean in this context? Could you give me some examples?

In this video, the word "extra" is used as an adverb, and it means to a greater extent than usual. "An extra good hair day" means that it will be a "good" hair day that is especially (or extra) good. Ex: My son is very well behaved today. He is trying to be extra good. Ex: The birthday present I bought for my sister is extra special. She has wished for it for a long time.

Is it okay to say "that's cheating!" instead of "no fair!" in this context?

Well, it's possible if it's against the rules! However, it seems like this is more of a "loophole" than "cheating." A "loophole" is a permittable or legal way to avoid or escape something or find another way to do it. And it's not fair since the other plans can't do this. If it was clearly against the rules, then yes, he could have said, "that's cheating!" Ex: I caught him trying to cheat during the card game. Ex: I found a loophole in the contract.

What does "bank holiday" mean? I don't think it has anything to do with a bank!

It does have a bit to do with a "bank"! A "bank holiday" is a public holiday when the banks are closed in the UK. But it means the same thing as a "public holiday." Ex: I'm looking forward to the next bank holiday so that I can visit my parents. Ex: We have a bank holiday coming up. Make sure you draw money beforehand.

What's "breakthrough" mean and when's it used?

A "breakthrough" means a sudden, dramatic, and important discovery or advance in knowledge and technique. It's used in relation to significant moments, as well as when a big success happens in one's life. Ex: The new vaccine was a medical breakthrough that doctors and scientists had worked on for years. Ex: Going to counseling is often a huge breakthrough for many people. Ex: Their album was a breakthrough and they soared to the top charts.

Can I replace "collect" with "pick up" in this context? What is the difference between those two?

Yes, you can. I am unsure about British English, but in American English we use "pick up" more frequently than "collect." There isn't a difference between the two phrases; they both mean the same thing in this context. "Collect" seems to be more formal than "pick up." Ex: I need to pick up my sister from the airport. Ex: She came to collect him from the train station. Ex: He plans to pick her up from the port. Ex: The carriage came to collect her.