Ok, these ones might not be as hard or as confusing as they look!
I believe most people understand their meanings but their usage in writing is another thing all together.
Where people tend to make the most mistakes is with the words too and to. Many times I'd read manuscripts at work with misuse of these two words.
Let's start with TOO -
"George copied a dozen transcripts for the meeting, but I will tell him to make extra copies for you too."
So how do you know which one to use when?
Well, the word too (an adverb), is almost always used at the end of a sentence. As a matter of fact, try substituting the word 'also' instead of too and it should mean the same thing. If it's used within a sentence, then it usually implies something used 'excessively' - you know, something that exceeds the normal or usual limit.
I have always been too busy to go to the museum.
It was too much for her to bear.
Ok, this one EVERYBODY knows! Two is the written form of the actual number 2.
There are two applicants for the job.
She has two cats.
So, that one was a bit more straight forward and should be easier to use in writting. Let's move on to the final one:
To is a preposition, which refers to a place, position or direction.
Let's go to the store.
Give it to me.
In its most common contexts, it is also used as part of infinitive verb phrases, such as in “to eat”, "to sleep", "to drive" etc.
So, to sum it all up, when unsure, use to, but if you mean additional (or also), or excessive - use too, and if you mean a numerical amount use two!