1. A = B (when two items are the same)
Chris is as tall as his brother.
She was as white as a sheet.
2. A > < B (when two items are NOT the same).
Her coffee is not as good as the coffee my mother makes.
3. When comparing two elements with using 'than'.
She makes fewer mistakes than you (do).
It was more expensive than I thought.
He is stronger than I expected.
4. When comparing two or more items we use the superlative of adjectives and the ... in/of:
This is the oldest buidling in New York.
This is the best pizza (that) I have ever eaten.
This is the worst film (that) I have ever seen.