can someone define superlatives for me? especially how they should be used?
Here is an extract from “A Writer’s Reference – by Diana Hacker:

“Use comparative to compare two things, the superlative to compare three or more.

To form comparatives and superlatives of most one- and two-syllable adjectives, use the endings -er and - -est: smooth, smoother, smoothest; easy, easier, easiest. With longer adjectives, use more and most: exciting, more exciting, most exciting.

Some one-syllable adverbs take the ending –er and –est (fast, faster, fastest), but longer adverbs and all of those ending in –ly form the comparative and superlative with more and most.
The comparative and superlative forms of the following adjectives and adverbs are irregular: good, better, best; bad, worse, worst; badly, worse, worst.

Do not use double comparatives or superlatives. When you have added ­ -er or ­-est to an adjective or adverb, do not use more or most. (EX: the happiest not the most happiest).

Do not use comparatives or superlatives with absolute concepts such as unique or perfect. Either something is unique or it isn’t. It is illogical to suggest that absolute concepts come in degrees.”
By the way, she also mentioned, "Most is colloquial when used to mean "almost" and should be avoided. Almost [not Most] everyone went to the parade."
The discussion about the meaning of most using as an adverb could be found at: http://pewebdic2.cw.idm.fr/display/display.html?unfolded=27796&ids=27796,27797,26019,26020,27795
oops, just a quick edit, what i meant was, can someone also explain the RULES as to how superlatives can be used.

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Superlatives are used for comparison. The superlative form of the adjective or adverb indicates that something has a quality to a greater degree than something else. Generally you only use superlatives when comparing 3 or more things, although sometimes it can be used for sets of two.
"John is tall"
"Peter is taller than John"
"Craig is the tallest " (tallest is the superlative)
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