Want can be followed by a 'to'-infinitive clause.
Such a clause may have a subject expressed, or may not. If it has, then the subject comes before the 'to' infinitive, and means that the speaker wants that subject to do whatever the clause says.
If there is no subject expressed, then the subject of the main clause is taken as the subject the infinitive clause.
I want to inform you that ...
means that I want myself to be the one who informs you of whatever.
I want you to inform him that ...
means that I want you to be the one who informs (him).
*I want you to inform that
is not grammatical, because "inform" requires an indirect object, and "you" can only be the subject.
With a verb that doesn't require an indirect object, both are grammatical, and have different meanings:
He wants to buy it.
means he wants himself to be the one who buys it.
He wants you to buy it.
means he wants you to be the one who buys it: 'you' is the subject of "buy".