As an adjective:
* "That new electric car is cool as a cucumber."
* "The movie was cool as ice, but the plot was confusing."
* "The band's music was cool as the breeze on a summer night."
As a conjunction:
* "I'd rather stay home and relax, cool as the other kids are going to the party."
* "I was feeling pretty nervous, cool as everyone else seemed so calm."
In idiomatic expressions:
* "I stayed cool as a cucumber during the interview."
* "The thief acted cool as a fox while stealing the money."
The best way to use "cool as" depends on the context and the desired meaning.