This word expresses direction or position. It's about the relationship between things.
So we can say, 'Give the parcel to her.'
The parcel is to be moved in her direction.
'Are you going to London?'
Are you moving to the place called London?
'You're going to be six tomorrow!'
With a movement in time (tomorrow) you are going to become six.
This means 'in addition to', 'as well as,' or 'to a greater degree than is usual or desirable'.
So we can say, 'Davy is going to London too.'
Davy is also moving in the direction of London.
Or we say, 'It's too hot in here.'
It is hotter than desirable here.
Or, 'It's too expensive.'
It costs more than I would like to spend.
A useful way of remembering which word to use is to think 'too much'. If what you mean is that something is too much - much too hot, much too cold, much too expensive - then use the word with the extra 'o'.
So - 'too much.'
NOT - 'to much.'
This is an entirely different word - it's the number two.
Why does it have a 'w' in the middle? Because the 'w' used to be pronounced.
The word used to be said, as it still is in Scotland, as 'twa'. Think of 'twin' which means 'double'. It's from the Old English twinn, which meant 'double' or 'two'.
So, if you don't know whether you should use 'two', ask yourself if you mean the number two, or something twinned or doubled.
The shepherd had two dogs.
NOT - the shepherd had to dogs
And NOT - the shepherd had too dogs.