Grammarly Speaking...

"To" is a word that is often mistaken or muddled up in analysis because it is small and has the ability to move around in sentences. While interviewing prospective English teachers, this error is revealed. Therefore, I think it is important to explain this concept.

The determinant of the function of 'to' is the word or phrase following the word.
For example,

a. I like to play outdoors
b. Adams threw a piece of bone to the dog

In sentence 'a', 'to' precedes a verb thus it is a particle which marks the following verb as an infinitive.
Other examples: to grow, to come, to get, to know e.t.c.

In sentence 'b', 'to' precedes a noun phrase. Hence, 'to' here functions as a preposition (showing the relationship between 'the dog' and other words in the sentence), pointing out who/what the bone was thrown to.
Other examples: to anyone, to me, to a great extent, to the tune of e.t.c.