The adverb too is used to show undesirable extremes. It has a negative meaning.

She is too fat.
He is too tired.

An infinitive structure is often used after too + adjective/adverb/determiner.

He is too tired to work.
It is too hot to go outside.
We arrived too late to have dinner.

Sometimes the infinitive may have its own subject. In such cases it is usually introduced by for.

It is too late for us to begin a new lesson.

Expressions used to modify comparative adjectives can also be used to modify too.

It happened a bit too soon.
She appeared a little too confident.

Note that before adjectives without nouns we use too, not too much.

You are too rude. (NOT You are too much rude.)
The news is too good to be true. (NOT The news is too much good to be true.)

Before adverbs we use too, not too much.

It arrived too late. (NOT It arrived too early.)

Note that we do not normally use too before an adjective followed by a noun.

I could not lift the bag because it was too heavy. (BUT NOT I could not lift the too heavy bag.)
I couldn’t solve the problem – it was too difficult. (BUT NOT I couldn’t solve the too difficult problem.)

Too and very

Too does not mean the same as very. Too means ‘more than is necessary’ or ‘more than is wanted’.
In an informal style, however, too is used to mean ‘very’.

That was really too kind of you. (= That was really very kind of you.)