What spanish letters sound like an English letter S?

The Spanish letter "c" sounds like an English "s" when it is followed by the letters "i" or "e"

Examples:

* "ce" as in "cielo" (sky)

* "ci" as in "ciudad" (city)

It's important to note that this rule only applies when the "c" is followed by "i" or "e." In other cases, "c" will be pronounced like a "k."