As with any subject of study, it is always helpful, nay, necessary to learn the terms of art that relate to the subject. In this case it will be easy since by simply knowing the definition of the word 'sarcasm' should be enough to point you in the right direction.
Sarcasm
Pronunciation: 'sär-"ka-z&m
Function: noun
Etymology: French or Late Latin; French sarcasme, from Late Latin sarcasmos, from Greek sarkasmos, from sarkazein to tear
flesh, bite the lips in rage, sneer, from sark-, sarx flesh; probably akin to Avestan thwar&s- to cut
1 : a sharp and often satirical or ironic utterance designed to cut or give pain
2 a : a mode of satirical wit depending for its effect on bitter, caustic, and often ironic language that is usually
directed against an individual b : the use or language of sarcasm (this is no time to indulge in sarcasm)
Definition courtesy of Merriam-Webster Online Dictionary
Note: If you are having trouble understanding the definition of the word 'sarcasm', perhaps your time would be best used tackling another field of study.
Exercise: Memorize the definition of the word 'sarcasm'. Make sure that you can recite it word for word, and at the same time understand what you are saying. This is very important, because the definition will be crucial in completing your next exercise.