Subject

The [main verb] of a clause happens for the subject: the subject can ‘act’ the verb or ‘experience’ the verb. Every clause must have one subject and one [finite verb].

A subject must be a noun. It can be any type of noun.
The dog is confusing.
She is confusing.
What you did is confusing.

For most personal pronouns, the subject form is different from the [object] form.
* I
* She
* He
* We
* They
The second person pronoun used to have a difference between subject and object and a difference between singular and plural, but we lost those differences about two hundred years ago.
* Thou
* Ye

If the subject is a plural noun or a group of nouns, the verb will take a plural form if it can.
They are confusing.
Bob and Sam are confusing.

A [prepositional phrase] cannot be a subject, and so the [verb] will be singular or plural depending upon the [noun] before the phrase.
The box of matches was wet.

In British English, the [verb] can be either singular or plural with a plural subject for a group of people. The singular form says that the group are absolutely united; the plural form says that they are different from each other.
My team is winning.
The government are stupid.