Use _er, _est if the adjective has one or two syllables, e.g. happy, happier, happiest; high, higher, highest.
Positive degree: high
Comparative degree: higher
Superlative degree; highest
Use more or most if the adjective has more than two syllables, e.g. beautiful, more beautiful, most beautiful.
There are also some words that have special comparative forms, e.g. good, better, best; bad, worse, worst.
every (adjective) = all the things referred to but it is treated as a singular, i.e. it is usually followed by a singular noun, e.g. Every boy in the class failed the test.
much + singular uncountable noun, e.g. much money.
many + plural countable noun, e.g. many boys.