Once you know how to form faster and the fastest, you need to choose the right form. A comparative adjective compares two nouns. A superlative adjective describes one noun as the highest or lowest member of a group.
Compare two things
Use a comparative adjective followed by than to compare two nouns. The nouns can name people, animals, places, or objects.
A tiger is faster than a lion.
Tokyo is bigger than Paris.
*Noun phrases.
*Comparative adjective.
*Comparison word.
In the first sentence, the nouns tiger and lion are compared by speed. In the second, the cities Tokyo and Paris are compared by size. The comparative adjectives faster and bigger show the difference. Than introduces the second noun.
Identify one member of a group
Use the plus a superlative adjective when one noun has the highest or lowest degree of a quality in a group. A phrase such as in the class names the group.
The cheetah is the fastest land animal in the world.
Mia is the youngest student in the class.
*Noun phrase.
*Superlative adjective with the definite article.
*Comparison group.
Fastest describes one land animal in a group of land animals. Youngest describes one student in a class. The pink phrases name the groups.
Check that the form matches the meaning
Use a comparative adjective with than when the sentence compares two nouns. Use a superlative adjective when it names one noun as the highest or lowest in a group. Even if three vehicles are present, you can still compare just two of them.
The bus is the biggest than the car.
The bus is bigger than the car.
The bus is bigger of the three vehicles.
The bus is the biggest of the three vehicles.
In the first pair, than the car compares two vehicles. In the second pair, of the three vehicles names the group, so the adjective must be superlative.
TOEFL strategy
Find the adjective first. If you see than, check for a comparative adjective. If the sentence identifies one noun in a group, check for the plus a superlative adjective. Make sure both sides of a comparison contain nouns of the same kind.