Sentences
比 for comparisons
比 goes between the two things being compared, and the adjective stays exactly as it is.
Adjectives never change shape in Chinese, so there is no taller or tallest to learn. A comparison is A 比 B adjective, and any amount goes after the adjective. There is no direct opposite of 比: for less, turn the sentence round or use 没有, which reads as does not have as much. 一样 covers sameness and pairs with 跟.
Examples
我比你高wǒ bǐ nǐ gāoI'm taller than you
他比我大两岁tā bǐ wǒ dà liǎng suìhe's two years older than methe amount comes last
我没有你高wǒ méiyǒu nǐ gāoI'm not as tall as you
这两个一样zhè liǎng gè yíyàngthese two are the same
Watch out
The mistake this causes
Leaving 很 in, as in 我比你很高. The 很 exists to stop a bare adjective sounding unfinished, and a comparison already finishes it.