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)