What is the main difference between single inverted comma and double inverted comma ?

the double quotation marks are used for direct quotes or for dialogues :

dialogue:

"hello , nice to meet you "

direct quote :

the man said , " i am fine ".

single quotes are used for emphasis :

so do you want to 'play' as well ?

note that you never put double quotes inside other double quotes, you have to use single quotes for the 'inside' quote

for ex :

"the boy said 'my sister is sick' "