It is cloudy today.

First of all, it it.

Simple meaning, rich usage, summed up for your reference:

Generally refers to inanimate objects or animals.

Learning is a bitter root, but it bears sweet fruit.

Learning is bitter and sweet.

2, you can refer to the baby, or you don't know the gender of the other party.

The baby is crying. It must be hungry. The baby is crying. It must be hungry.

3. Something about it (judging from the context, what does it mean)

Relax.

Relax.

4. Being the subject refers to time, date, distance, weather, etc. It is a personal pronoun.

It is snowing on the mountain.

5. Formal subject

The real subject may be infinitive, gerund or subject clause, usually postpositioned.

6. Formal objects

The real object can be infinitive, gerund or object clause, usually postpositioned.

Second, it is cloudy.

Cloudy; Yin; Turbidity; Ambiguity; Doped with white; Not sure; Opaque; Blinded with tears; Fuzzy

1. Cloudy sky

A gloomy day; cloudy day

2. Cloudy nights

Cloudy night