Countable and Non-Countable nouns

Countable nouns are those which can be counted, they also have singular as well as plural forms.
Countable nouns are used with a,an,the,many,few,fewer,number,this,that,every,each, neither,either,those,these,some,any,enough
For example - She made fewer mistakes in the match today

While non-countable or Mass nouns are those which can't be counted and sometime they do not have any plural form.
Non-countable nouns are used with much,less/lesser,this,that,some,any,enough,amount of
For example - Arun have less money than suresh

Some of the nouns can be used as both Countable and non countable ones. It just depends upon how we are using them.
For example-  he got into trouble(non-countable)
                       he had many troubles(countable)

the usage of 's and s'

Apostrophe ( ' ) and letter ( s ) is used to make a noun possessive.

For example - That car is amit's
                        The men's hockey match is tomorrow.

• A singular noun can use 's and s' for same effect. 

For example - The car's speed is slow               correct
                        The cars' speed is slow               correct

• A Plural ending with s takes apostrophe( ' ) to become possessive.

For example - The new buses's are fast              correct
                        The new buses's are fast              incorrect

Common mistakes in Grammer

• The usage of    's and s'