Quick answer
С с is the s of “see”, in every position. The k sound is written К к.
Сс
Сс
s
спаси́боthank you
How to say it
A plain s. Before a voiced consonant it turns to z: сде́лать sounds like “zdelat”.
спаси́боthank you
сестра́sister
супsoup
сырcheese
столtable
сейча́сright now
С as a preposition
Alone, с means “with” and takes the instrumental: с молоко́м (with milk), со мной (with me). It also means “from (a surface)” with the genitive: со стола́. Before awkward clusters it becomes со.
CCCP
The old Soviet abbreviation СССР is read “es-es-es-er”. Latin readers guess “see-see-see-pee” — a good reminder that С is s and Р is r.
Typical mistakes
Reading суп as “kup”
“soop”
С is never a k sound.
с мной
со мной
The preposition takes an extra о before certain clusters.
Check yourself
Which word contains С?
спаси́бо — thank you.