Learn English – Which preposition is correct here

You have understood one thing correctly: a preposition is combined with what follows it to form a prepositional phrase, and they form a single constituent in the sentence. Generally speaking, words in English govern (ie. control or specify) the words that come after them. In linguistics, we say that English is right-branching, meaning that new syntactic elements come after (to the right of, in writing) the elements that govern them.

Note that there are exceptions, such as adjectives, which precede the nouns that govern them. English is not exclusively right-branching, but it is predominantly right-branching.

But what does this have to do with prepositions? Well, just as a preposition governs the noun phrase that comes to its right, the preposition itself is governed by something to its left. And in many cases, that thing is a verb. English is full of idiomatic combinations of verb + preposition, where the verb requires a specific preposition to follow it, and anything else is an error. To take some obvious examples cribbed from other answers:

I converse with you. [Not to/at/of you]

They rely on the bus. [Not with/to/at the bus]

These combinations are highly idiomatic, meaning that the correct choice of preposition cannot be predicted simply by knowing the general meaning of the words involved. So the people who ask about what preposition follows a certain word are asking a reasonable and intelligent question. The choice of preposition very, very often depends on what came before it.

Some of the style guides that I have are categorical in claiming that the plural verb is correct in such constructions as:

One of the things that makes/make him great is he brings it every night.

Follet in Modern American Usage (p298) states:

These words (one of the [plural noun] who .. ) introduce the most widespread of all defiances of rudimentary grammar: the coupling of a plural subject with a singular verb.

Partridge in Usage and Abusage (p214) states:

The rule is that the formula, one of + plural noun, requires the ensuing verb to be plural.

The Right Word at the Right Time (p405) states:

The construction one of those who or one of the Xs that often presents the writer or speaker with a problem: does the verb that follows go into the singular or the plural? ... The answer is the plural: who or that refers not to one but to those or the Xs. (* See below)

Garner in Modern American Usage (p590) writes:

This construction requires a plural verb in the relative clause, not a singular one.

Other style guides offer a more nuanced approach. For example, the conclusion after a lengthy discussion of the construction in Merriam Webster's Dictionary of English Usage (p690) is:

So the choice of a singular or plural verb ... is a matter of notional agreement: is one or those (Xs) to be the master? .... There is abundant evidence that one has controlled number in modern English sentences from Shakespeare to James Kilpatrick, and there is likewise abundant evidence that those has controlled number in other sentences. Addison was not troubled by using both constructions. You need not be more diffident than Addison.

Peters in The Cambridge Guide to English Usage (p394) states:

For most writers the choice depends on whether you're thinking of a single case or a general principle. Usage commentators in the UK and the US have been inclined to say it should be the plural; and the Harper-Heritage usage panel voted heavily in its favor (78%). Yet Webster's English Usage (1989) found ample American evidence for the singular construction, and it's just as common as the plural in British data from the BNC. Writers using the singular take their cue from one, whereas plural users are responding to those [people] or the [things].

Finally, Steven Pinker, in his recent The Sense of Style (p250) writes:

For more than a thousand years the siren song of the singular one has overridden the syntactic demand of the plural those, and writer after writer has gone with the singular.

...

Usage guides today suggest that either the singular or plural is acceptable in this construction, depending on whether one or those looms larger in the writer's mind.

It is interesting that one of the sentences that The Right Word at the Right Time lists as ungrammatical is the following:

If you are one of those listeners who is alternately worried and puzzled by the state of modern English ... .

This sentence was written by pre-eminent British linguist Professor David Crystal.