Using "it" at the beginning of a sentence

Question

It can be difficult to talk about subjects like XXXX.

It can be difficult to learn a new language.

I hope it doesn't rain Today.

What does it means in the above sentences?
Why should we start the sentences with it?

Answer 1

It in those sentences is called dummy pronoun: It is used without any reference to any agent, but it is syntactically required.

The first sentence could be rephrased as "Talking about subjects like XXXX can be difficult." while the second sentence could be rephrased as "Learning a new language can be difficult." The difference between the original sentences and the one I am suggesting is the word order. With the original sentences, the first words are "It can be difficult"; that could be done to put those words in evidence.

With sentences about weather, the verb (e.g. rain, snow) is impersonal, and intransitive. Since in English the subject of a sentence is normally not implicit, it is used. (In English you don't normally write a sentence like "Is playing football with his friends." or "Rains.")