Comparison Study these example:
How shall we travel? By car or by train?
Let's go by car. It's cheaper.
Don't go by train. It's more expensive.
Cheaper and more expensive are comparative forms.
After comparatives you can use than:
It's cheaper to go by car than by train.
Going by train is more expensive than going by car.

The comparative form is -er or more ... .
We use -er for short words(one syllable):
cheap -> cheaper fast -> faster
large -> larger thin -> thinner
We also use -er for two-syllable words that end in -y (-y -> ier):
lucky -> luckier early -> earlier
easy -> easier pretty -> prettier
We use more ... for longer words(two syllables or more):
more expensive, more often, more comfortable
We also use more... for adverbs that end in -ly:
more slowly, more seriously, more carefully
You can use -er or more... with some two-syllable adjectives, especially:
clever, narrow, quite, shallow, simple
It's too noisy here. Can we go somewhere quieter/more quiet?
good/well -> better
bad/badly -> worse: far -> further(or farther):