In the developer's guide it says you can create it in the Flow Editor view, click Insert Skill> Slot, but I don't see that option.

you're looking at the documentation for v12 - if you're building on botpress cloud that option isn't present

so, how can I create slots in botpress cloud?

what are you trying to do?

I have a list of intents, where, for example, one of the phrases is 'I want to fly to Italy,' and I want the word 'Italy' to be able to be any other city, because if I ask the chatbot a question that goes beyond the defined intents, it doesn't understand. I don't know how I could solve this

do you mean you want to extract the city from a user's input?

yes