We use than to compare two things with each other.
For example: This fall is colder than last year.
Attention: Note that 'than' is different from 'then'. 'Than' is actually used for comparisons while 'Then' is used as an adverb, to indicate an actions in time.
We use and to describe a change of someone or something.
For example: The climate is getting warmer and warmer.
As in example one, 'and' is placed between two comparative adjectives to indicate that the car is both better and more expensive than another car. In this context, 'and' is used to add something more about the car.
We use the when something depends on another.
For example: The more you give away your money, the poorer you'll get.