Key Difference: ‘To’ is a preposition that can imply many different things depending on the usage in a particular sentence. ‘Too’ is used to express the intensity of a particular situation, similar to an adjective.

‘To’ and ‘too’ are very similar in their spelling, but are completely different when it comes to usage. They mean different things in different contexts and should not be used interchangeably.

‘To’ is a preposition that can imply many different things depending on the usage in a particular sentence. In certain sentences it is used in dative case when declension nouns, it can imply going to a certain destination, it can imply a state of achieving and it can be used to refer to a certain person or a receiver of an object. The word ‘to’ can also indicate a relationship between two people, when it is used in certain contexts or it can be used to indicate a comparison between two things.

Oxford Dictionary defines ‘to’ as:

• expressing motion in the direction of (a particular location)
• expressing location, typically in relation to a specified point of reference
• expressing a point reached at the end of a range or after a period of time
• (in telling the time) before (the hour specified)
• approaching or reaching (a particular condition)
• expressing the result of a process or action
• governing a phrase expressing someone’s reaction to something
• identifying the person or thing affected by or receiving something
• identifying a particular relationship between one person and another
• indicating that two things are attached or linked
• concerning or likely to concern (something)
• used to introduce the second element in a comparison
• expressing purpose or intention
• expressing an outcome or result
• expressing a cause
• indicating a desired or advisable action
• indicating a proposition that is known, believed, or reported about a specified person or thing
• forming a future tense with reference to the immediate future
• after a noun, indicating its function or purpose
• after a phrase containing an ordinal number
• used without a verb following when the missing verb is clearly understood

Examples of 'to':

• This is my first visit to Australia.
• The camp is forty miles to the south of the site
• The company’s accounts showed a drop in profits from £105 m to around £75 m
• It is five to eight (time).
• Christopher’s expression changed from amazement to joy
• The vase was smashed to smithereens
• To her astonishment, he smiled at her.
• They donated $400 to the hospital.
• He is married to his cousin Emily.
• He is younger to his sister by 3 years.
• My car only does ten miles to the gallon.
• He had left his dog tied to a drainpipe.
• The missiles are a threat to world peace.
• I have to go out to get a few things.
• I managed to return to my previous home.
• I’d love to go to London this summer.
• People believe the old hospital to be haunted.
• Would you like something to drink?

‘Too’ is used to express the intensity of a particular situation, similar to an adjective. It can also be used to convey the meaning of ‘also’ and ‘very’.

Oxford Dictionary defines ‘too’ as:

• to a higher degree than is desirable, permissible, or possible; excessively
• informal very
• in addition; also

Examples of ‘too’:

• The car was driving too fast.
• The sun is too bright.
• The dress was two sizes too small for her.
• Too bad!
• Is he coming too?
• He was too sure about himself in the meeting.

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