What stands for the term, International English Language Testing System, is accepted widely, means globally. They are of two types, for you to drive, Academic for study, and General for duty. Has a four components, equally worthy distributions, the Listening and Reading, Writing and Speaking. All are interrelated, and inter-connected, listening requires concentration, reading needs comprehension. Speaking means fluency, neither a rapidity, writing requires lexical resource, nor a lengthy discourse. Preparation is tough, you may feel flop, but with careful effort, never let you drop. At the end, the score you receive, called as band score, you need a roar. Sometime these band score, may bend your core, but with conscious learning, you may bend the band earning. If it clicks your interest, we'll talk on rest, I'll try my best, good luck for your test!