You can’t use “to” instead of “too” and vice versa. “To” is a preposition with several meanings, including “toward” and “until.” “Too” is an adverb that can mean “very” or “also.” Just to be clear: “two” is pronounced the same as “to” and “too,” but it can’t be used instead of either of them because it’s a number.
In the hierarchy of things that drive grammar sticklers mad, to and too are near the top. It’s very common to see them confused, abused, and misused, and not just in YouTube comment sections or on Reddit. People seem to mix up these two funny little words all over the place, and it’s something that can happen to anyone.
What Seems to Be the Problem Here?
Apart from being spelled very similarly, to and too are pronounced the same—[too]. We call words that share a pronunciation homophones, and if you take a look at any list of commonly confused words, you’ll find plenty of homophones on it. Words like there, their, and they’re, your and you’re, and bear and bare are up there, along with to and too—and their third homophone, two. It doesn’t matter whether the homophones have different meanings and uses or if they are in completely different word classes; we still mix them up.
The only way to fix this is to repeat over and over again what each of the homophones means so that people who don’t know it get the chance to learn. For those who know the difference, a few minutes of proofreading should fix the issue.
What Does To Mean, and How Should I Use It?
To is a preposition and a versatile little word that can be used to say many things. We’ll name a few:
To indicate the goal or direction of a movement, as well as a place of arrival:
Crucially the FCO stopped well short of advising against travel to France, which is the most popular holiday destination in the world (and the second-most popular, after Spain, for UK holidaymakers).
To indicate that the verb following it is an infinitive:
Had David Cameron not won an election he never expected to win, he might not have lost a referendum he never expected to lose.
To indicate possession, attachment, additions, and other kinds of relationships between words:
Real Madrid superstar Gareth Bale has announced his engagement to long-term girlfriend Emma Rhys-Jones.
—The Daily Mirror
To indicate a range or a period of time:
What Does Too Mean, and How Should I Use It?
Too is also a useful little word, but it’s not a preposition like to, and it doesn’t have as many meanings:
It can be used instead of “besides,” “in addition,” “also,” or “as well”:
But from what we’ve seen in this tournament I think she meant it, too.
It can be used to indicate excessiveness:
Chances are that too much information running through our small brains clouds our thinking, making it more difficult to do our jobs.
It can be used instead of “very”:
On the other hand, given that these references are too obvious, they may have been intentionally included to insinuate a Kemalist junta rather than a Gulenist one.
How To Stay Safe When Using To and Too
Since they are pronounced the same, you don’t have to worry about mixing up to and too in speech. It’s writing that creates problems. But there’s an easy way to make sure that the correct word is being used. Because to can be used in more ways than too, it would be easier to remember that too can be replaced with “as well,” “very,” or “excessively.” If you’re not sure whether the to you’ve written might actually be a too, try replacing it with one of the words too substitutes. If it works, you’ve made a mistake. If it doesn’t, you’re good. You can do the same to make sure that your toos are indeed toos and not tos.
from Grammarly Blog https://www.grammarly.com/blog/to-too/