Here are some examples of alliteration using the letter "s":
* Slippery snakes slide silently through the grass. (This uses the "s" sound at the beginning of "slippery", "snakes", "slide", and "silently")
* Seven swans swam serenely on the surface. (This uses the "s" sound at the beginning of "seven", "swans", "swam", and "serenely")
* She sells seashells by the seashore. (This is a classic example, using the "s" sound in "she", "sells", "seashells", and "seashore")
Remember that alliteration can be created with the "s" sound even when the actual letter written isn't "s," like in "shadow" or "ship" (which both have the "sh" sound).