Superlative adjectives are ones that compare three or more objects and that indicate the highest or lowest level of a certain quality. They generally (but not always!) end with the suffix -est. Hottest, coldest, best, and worst are some examples of superlative adjectives.
To check if an adjective is superlative, identify its basic form (e.g. hot, cold, good, bad for the four examples above), then see if it makes sense to replace the adjective with "most _____". For example, in the sentence "That was the hottest day this year," try replacing "hottest" with "most hot" to form "That was the most hot day this year." If the modified sentence still makes sense, you're looking at a superlative!
In general, adjectives have three forms: the standard form (the base form, such as good, bad, hot, or cold), the comparative form (which usually ends in -er and means "more _____" -- for example, hotter means "more hot"), and the superlative form. For example, the forms of the adjective nice are nice, nicer, and nicest.
Using this information, you should be able to figure out the superlative words for yourself! In case you can't, I've copied the passage below. I've italicized comparative adjectives and bolded superlative adjectives.
Ellen finished the race faster than Marybeth, but she was not always the fastest. She could remember many times that Eric ran faster than both of them and other times when she was the slowest in the whole fifth grade class. She was not feeling her best that day, though, so she thought that she would probably never run that slowly again.
The key is to remember that faster is comparative (as it compares two people--in the first sentence, for example, it compares Marybeth and Ellen), while fastest is superlative (as it means "most fast"). Similarly, slowest and best are superlative. (Best is the superlative form of the word good.) Note that "slowly" is an adverb, not an adjective!
The superlative adjectives are fastest, slowest, and best.