Words with no possesstion are just s.
Singular words with possession are 's.
Plural words with possesstion are s'.
Names, whether they end in s or not are always 's.
Names ending with s using 's like Luis's or Chaos's is a British English thing, which has spread around the commonwealth, hence Ako agrees with me. Using s' is the American English was of doing it. Depending on where you are in the world, and how you speak the English language will depend on how you say it. Although personally I'd use the English way of speaking English. As air said though, both are correct in universal English.
#getgoogled