This is jargon in English, and the answer varies depending on location.
One common way to say "That's cool" or "How Cool!" is Que Guay
In Spain, another way to say that something is really cool, you can say "____ es la leche." You can, of course, change that depending on the subject (by conjugating ser differently)
I am cool - soy fresco
soy cool
fresco/a
fresco/a
you say: "puedes calmarte?"
Es chido.
"Genial" or "chido"
!chido nombre!
Aguas frescos.
fresco, tibio = cool (adjective) refrescar = to cool
eso es genial.
super-guay